From 5ca9f4270c250a60a37d2e288be146515655f075 Mon Sep 17 00:00:00 2001 From: Andy Rothfusz Date: Thu, 23 Jan 2014 18:59:00 -0800 Subject: [PATCH 1/2] Fix 2720 -- Expanded documentation for docker run. Docker-DCO-1.1-Signed-off-by: Andy Rothfusz (github: metalivedev) Upstream-commit: 07c4eda46a6a1af82b4b519d9186b9bf7881d7cc Component: engine --- .../engine/docs/sources/articles/index.rst | 1 + .../docs/sources/articles/runmetrics.rst | 469 ++++++++++++++++++ .../engine/docs/sources/reference/builder.rst | 8 +- .../sources/reference/commandline/cli.rst | 39 ++ .../engine/docs/sources/reference/index.rst | 1 + .../engine/docs/sources/reference/run.rst | 353 +++++++++++++ 6 files changed, 867 insertions(+), 4 deletions(-) create mode 100644 components/engine/docs/sources/articles/runmetrics.rst create mode 100644 components/engine/docs/sources/reference/run.rst diff --git a/components/engine/docs/sources/articles/index.rst b/components/engine/docs/sources/articles/index.rst index 2cfc427420..75c0cd3fa9 100644 --- a/components/engine/docs/sources/articles/index.rst +++ b/components/engine/docs/sources/articles/index.rst @@ -12,3 +12,4 @@ Articles security baseimages + runmetrics diff --git a/components/engine/docs/sources/articles/runmetrics.rst b/components/engine/docs/sources/articles/runmetrics.rst new file mode 100644 index 0000000000..f7406bc5ed --- /dev/null +++ b/components/engine/docs/sources/articles/runmetrics.rst @@ -0,0 +1,469 @@ +:title: Runtime Metrics +:description: Measure the behavior of running containers +:keywords: docker, metrics, CPU, memory, disk, IO, run, runtime + +.. _run_metrics: + + +Runtime Metrics +=============== + +Linux Containers rely on `control groups +`_ which +not only track groups of processes, but also expose metrics about CPU, +memory, and block I/O usage. You can access those metrics and obtain +network usage metrics as well. This is relevant for "pure" LXC +containers, as well as for Docker containers. + +Control Groups +-------------- + +Control groups are exposed through a pseudo-filesystem. In recent +distros, you should find this filesystem under +``/sys/fs/cgroup``. Under that directory, you will see multiple +sub-directories, called devices, freezer, blkio, etc.; each +sub-directory actually corresponds to a different cgroup hierarchy. + +On older systems, the control groups might be mounted on ``/cgroup``, +without distinct hierarchies. In that case, instead of seeing the +sub-directories, you will see a bunch of files in that directory, and +possibly some directories corresponding to existing containers. + +To figure out where your control groups are mounted, you can run: + +:: + + grep cgroup /proc/mounts + +.. _run_findpid: + +Ennumerating Cgroups +-------------------- + +You can look into ``/proc/cgroups`` to see the different control group +subsystems known to the system, the hierarchy they belong to, and how +many groups they contain. + +You can also look at ``/proc//cgroup`` to see which control +groups a process belongs to. The control group will be shown as a path +relative to the root of the hierarchy mountpoint; e.g. ``/`` means +“this process has not been assigned into a particular group”, while +``/lxc/pumpkin`` means that the process is likely to be a member of a +container named ``pumpkin``. + +Finding the Cgroup for a Given Container +---------------------------------------- + +For each container, one cgroup will be created in each hierarchy. On +older systems with older versions of the LXC userland tools, the name +of the cgroup will be the name of the container. With more recent +versions of the LXC tools, the cgroup will be ``lxc/.`` + +For Docker containers using cgroups, the container name will be the +full ID or long ID of the container. If a container shows up as +ae836c95b4c3 in ``docker ps``, its long ID might be something like +``ae836c95b4c3c9e9179e0e91015512da89fdec91612f63cebae57df9a5444c79``. You +can look it up with ``docker inspect`` or ``docker ps -notrunc``. + +Putting everything together to look at the memory metrics for a Docker +container, take a look at ``/sys/fs/cgroup/memory/lxc//``. + +Metrics from Cgroups: Memory, CPU, Block IO +------------------------------------------- + +For each subsystem (memory, cpu, and block i/o), you will find one or +more pseudo-files containing statistics. + +Memory Metrics: ``memory.stat`` +............................... + +Memory metrics are found in the "memory" cgroup. Note that the memory +control group adds a little overhead, because it does very +fine-grained accounting of the memory usage on your system. Therefore, +many distros chose to not enable it by default. Generally, to enable +it, all you have to do is to add some kernel command-line parameters: +``cgroup_enable=memory swapaccount=1``. + +The metrics are in the pseudo-file ``memory.stat``. Here is what it +will look like: + +:: + + cache 11492564992 + rss 1930993664 + mapped_file 306728960 + pgpgin 406632648 + pgpgout 403355412 + swap 0 + pgfault 728281223 + pgmajfault 1724 + inactive_anon 46608384 + active_anon 1884520448 + inactive_file 7003344896 + active_file 4489052160 + unevictable 32768 + hierarchical_memory_limit 9223372036854775807 + hierarchical_memsw_limit 9223372036854775807 + total_cache 11492564992 + total_rss 1930993664 + total_mapped_file 306728960 + total_pgpgin 406632648 + total_pgpgout 403355412 + total_swap 0 + total_pgfault 728281223 + total_pgmajfault 1724 + total_inactive_anon 46608384 + total_active_anon 1884520448 + total_inactive_file 7003344896 + total_active_file 4489052160 + total_unevictable 32768 + +The first half (without the ``total_`` prefix) contains statistics +relevant to the processes within the cgroup, excluding +sub-cgroups. The second half (with the ``total_`` prefix) includes +sub-cgroups as well. + +Some metrics are "gauges", i.e. values that can increase or decrease +(e.g. swap, the amount of swap space used by the members of the +cgroup). Some others are "counters", i.e. values that can only go up, +because they represent occurrences of a specific event (e.g. pgfault, +which indicates the number of page faults which happened since the +creation of the cgroup; this number can never decrease). + +cache + the amount of memory used by the processes of this control group + that can be associated precisely with a block on a block + device. When you read and write files from and to disk, this amount + will increase. This will be the case if you use "conventional" I/O + (``open``, ``read``, ``write`` syscalls) as well as mapped files + (with ``mmap``). It also accounts for the memory used by ``tmpfs`` + mounts, though the reasons are unclear. + +rss + the amount of memory that *doesn't* correspond to anything on + disk: stacks, heaps, and anonymous memory maps. + +mapped_file + indicates the amount of memory mapped by the processes in the + control group. It doesn't give you information about *how much* + memory is used; it rather tells you *how* it is used. + +pgpgin and pgpgout + correspond to *charging events*. Each time a page is "charged" + (=added to the accounting) to a cgroup, pgpgin increases. When a + page is "uncharged" (=no longer "billed" to a cgroup), pgpgout + increases. + +pgfault and pgmajfault + indicate the number of times that a process of the cgroup triggered + a "page fault" and a "major fault", respectively. A page fault + happens when a process accesses a part of its virtual memory space + which is inexistent or protected. The former can happen if the + process is buggy and tries to access an invalid address (it will + then be sent a ``SIGSEGV`` signal, typically killing it with the + famous ``Segmentation fault`` message). The latter can happen when + the process reads from a memory zone which has been swapped out, or + which corresponds to a mapped file: in that case, the kernel will + load the page from disk, and let the CPU complete the memory + access. It can also happen when the process writes to a + copy-on-write memory zone: likewise, the kernel will preempt the + process, duplicate the memory page, and resume the write operation + on the process' own copy of the page. "Major" faults happen when the + kernel actually has to read the data from disk. When it just has to + duplicate an existing page, or allocate an empty page, it's a + regular (or "minor") fault. + +swap + the amount of swap currently used by the processes in this cgroup. + +active_anon and inactive_anon + the amount of *anonymous* memory that has been identified has + respectively *active* and *inactive* by the kernel. "Anonymous" + memory is the memory that is *not* linked to disk pages. In other + words, that's the equivalent of the rss counter described above. In + fact, the very definition of the rss counter is **active_anon** + + **inactive_anon** - **tmpfs** (where tmpfs is the amount of memory + used up by ``tmpfs`` filesystems mounted by this control + group). Now, what's the difference between "active" and "inactive"? + Pages are initially "active"; and at regular intervals, the kernel + sweeps over the memory, and tags some pages as "inactive". Whenever + they are accessed again, they are immediately retagged + "active". When the kernel is almost out of memory, and time comes to + swap out to disk, the kernel will swap "inactive" pages. + +active_file and inactive_file + cache memory, with *active* and *inactive* similar to the *anon* + memory above. The exact formula is cache = **active_file** + + **inactive_file** + **tmpfs**. The exact rules used by the kernel to + move memory pages between active and inactive sets are different + from the ones used for anonymous memory, but the general principle + is the same. Note that when the kernel needs to reclaim memory, it + is cheaper to reclaim a clean (=non modified) page from this pool, + since it can be reclaimed immediately (while anonymous pages and + dirty/modified pages have to be written to disk first). + +unevictable + the amount of memory that cannot be reclaimed; generally, it will + account for memory that has been "locked" with ``mlock``. It is + often used by crypto frameworks to make sure that secret keys and + other sensitive material never gets swapped out to disk. + +memory and memsw limits + These are not really metrics, but a reminder of the limits applied + to this cgroup. The first one indicates the maximum amount of + physical memory that can be used by the processes of this control + group; the second one indicates the maximum amount of RAM+swap. + +Accounting for memory in the page cache is very complex. If two +processes in different control groups both read the same file +(ultimately relying on the same blocks on disk), the corresponding +memory charge will be split between the control groups. It's nice, but +it also means that when a cgroup is terminated, it could increase the +memory usage of another cgroup, because they are not splitting the +cost anymore for those memory pages. + +CPU metrics: ``cpuacct.stat`` +............................. + +Now that we've covered memory metrics, everything else will look very +simple in comparison. CPU metrics will be found in the ``cpuacct`` +controller. + +For each container, you will find a pseudo-file ``cpuacct.stat``, +containing the CPU usage accumulated by the processes of the +container, broken down between ``user`` and ``system`` time. If you're +not familiar with the distinction, ``user`` is the time during which +the processes were in direct control of the CPU (i.e. executing +process code), and ``system`` is the time during which the CPU was +executing system calls on behalf of those processes. + +Those times are expressed in ticks of 1/100th of second. Actually, +they are expressed in "user jiffies". There are ``USER_HZ`` +*"jiffies"* per second, and on x86 systems, ``USER_HZ`` is 100. This +used to map exactly to the number of scheduler "ticks" per second; but +with the advent of higher frequency scheduling, as well as `tickless +kernels `_, the number of kernel +ticks wasn't relevant anymore. It stuck around anyway, mainly for +legacy and compatibility reasons. + +Block I/O metrics +................. + +Block I/O is accounted in the ``blkio`` controller. Different metrics +are scattered across different files. While you can find in-depth +details in the `blkio-controller +`_ +file in the kernel documentation, here is a short list of the most +relevant ones: + +blkio.sectors + contain the number of 512-bytes sectors read and written by the + processes member of the cgroup, device by device. Reads and writes + are merged in a single counter. + +blkio.io_service_bytes + indicates the number of bytes read and written by the cgroup. It has + 4 counters per device, because for each device, it differentiates + between synchronous vs. asynchronous I/O, and reads vs. writes. + +blkio.io_serviced + the number of I/O operations performed, regardless of their size. It + also has 4 counters per device. + +blkio.io_queued + indicates the number of I/O operations currently queued for this + cgroup. In other words, if the cgroup isn't doing any I/O, this will + be zero. Note that the opposite is not true. In other words, if + there is no I/O queued, it does not mean that the cgroup is idle + (I/O-wise). It could be doing purely synchronous reads on an + otherwise quiescent device, which is therefore able to handle them + immediately, without queuing. Also, while it is helpful to figure + out which cgroup is putting stress on the I/O subsystem, keep in + mind that is is a relative quantity. Even if a process group does + not perform more I/O, its queue size can increase just because the + device load increases because of other devices. + +Network Metrics +--------------- + +Network metrics are not exposed directly by control groups. There is a +good explanation for that: network interfaces exist within the context +of *network namespaces*. The kernel could probably accumulate metrics +about packets and bytes sent and received by a group of processes, but +those metrics wouldn't be very useful. You want per-interface metrics +(because traffic happening on the local ``lo`` interface doesn't +really count). But since processes in a single cgroup can belong to +multiple network namespaces, those metrics would be harder to +interpret: multiple network namespaces means multiple ``lo`` +interfaces, potentially multiple ``eth0`` interfaces, etc.; so this is +why there is no easy way to gather network metrics with control +groups. + +Instead we can gather network metrics from other sources: + +IPtables +........ + +IPtables (or rather, the netfilter framework for which iptables is +just an interface) can do some serious accounting. + +For instance, you can setup a rule to account for the outbound HTTP +traffic on a web server: + +:: + + iptables -I OUTPUT -p tcp --sport 80 + + +There is no ``-j`` or ``-g`` flag, so the rule will just count matched +packets and go to the following rule. + +Later, you can check the values of the counters, with: + +:: + + iptables -nxvL OUTPUT + +Technically, ``-n`` is not required, but it will prevent iptables from +doing DNS reverse lookups, which are probably useless in this +scenario. + +Counters include packets and bytes. If you want to setup metrics for +container traffic like this, you could execute a ``for`` loop to add +two ``iptables`` rules per container IP address (one in each +direction), in the ``FORWARD`` chain. This will only meter traffic +going through the NAT layer; you will also have to add traffic going +through the userland proxy. + +Then, you will need to check those counters on a regular basis. If you +happen to use ``collectd``, there is a nice plugin to automate +iptables counters collection. + +Interface-level counters +........................ + +Since each container has a virtual Ethernet interface, you might want +to check directly the TX and RX counters of this interface. You will +notice that each container is associated to a virtual Ethernet +interface in your host, with a name like ``vethKk8Zqi``. Figuring out +which interface corresponds to which container is, unfortunately, +difficult. + +But for now, the best way is to check the metrics *from within the +containers*. To accomplish this, you can run an executable from the +host environment within the network namespace of a container using +**ip-netns magic**. + +The ``ip-netns exec`` command will let you execute any program +(present in the host system) within any network namespace visible to +the current process. This means that your host will be able to enter +the network namespace of your containers, but your containers won't be +able to access the host, nor their sibling containers. Containers will +be able to “see” and affect their sub-containers, though. + +The exact format of the command is:: + + ip netns exec + +For example:: + + ip netns exec mycontainer netstat -i + +``ip netns`` finds the "mycontainer" container by using namespaces +pseudo-files. Each process belongs to one network namespace, one PID +namespace, one ``mnt`` namespace, etc., and those namespaces are +materialized under ``/proc//ns/``. For example, the network +namespace of PID 42 is materialized by the pseudo-file +``/proc/42/ns/net``. + +When you run ``ip netns exec mycontainer ...``, it expects +``/var/run/netns/mycontainer`` to be one of those +pseudo-files. (Symlinks are accepted.) + +In other words, to execute a command within the network namespace of a +container, we need to: + +* find out the PID of any process within the container that we want to + investigate; +* create a symlink from ``/var/run/netns/`` to + ``/proc//ns/net`` +* execute ``ip netns exec ....`` + +Please review :ref:`run_findpid` to learn how to find the cgroup of a +pprocess running in the container of which you want to measure network +usage. From there, you can examine the pseudo-file named ``tasks``, +which containes the PIDs that are in the control group (i.e. in the +container). Pick any one of them. + +Putting everything together, if the "short ID" of a container is held +in the environment variable ``$CID``, then you can do this:: + + TASKS=/sys/fs/cgroup/devices/$CID*/tasks + PID=$(head -n 1 $TASKS) + mkdir -p /var/run/netns + ln -sf /proc/$PID/ns/net /var/run/netns/$CID + ip netns exec $CID netstat -i + + +Tips for high-performance metric collection +------------------------------------------- + +Note that running a new process each time you want to update metrics +is (relatively) expensive. If you want to collect metrics at high +resolutions, and/or over a large number of containers (think 1000 +containers on a single host), you do not want to fork a new process +each time. + +Here is how to collect metrics from a single process. You will have to +write your metric collector in C (or any language that lets you do +low-level system calls). You need to use a special system call, +``setns()``, which lets the current process enter any arbitrary +namespace. It requires, however, an open file descriptor to the +namespace pseudo-file (remember: that’s the pseudo-file in +``/proc//ns/net``). + +However, there is a catch: you must not keep this file descriptor +open. If you do, when the last process of the control group exits, the +namespace will not be destroyed, and its network resources (like the +virtual interface of the container) will stay around for ever (or +until you close that file descriptor). + +The right approach would be to keep track of the first PID of each +container, and re-open the namespace pseudo-file each time. + +Collecting metrics when a container exits +----------------------------------------- + +Sometimes, you do not care about real time metric collection, but when +a container exits, you want to know how much CPU, memory, etc. it has +used. + +Docker makes this difficult because it relies on ``lxc-start``, which +carefully cleans up after itself, but it is still possible. It is +usually easier to collect metrics at regular intervals (e.g. every +minute, with the collectd LXC plugin) and rely on that instead. + +But, if you'd still like to gather the stats when a container stops, +here is how: + +For each container, start a collection process, and move it to the +control groups that you want to monitor by writing its PID to the +tasks file of the cgroup. The collection process should periodically +re-read the tasks file to check if it's the last process of the +control group. (If you also want to collect network statistics as +explained in the previous section, you should also move the process to +the appropriate network namespace.) + +When the container exits, ``lxc-start`` will try to delete the control +groups. It will fail, since the control group is still in use; but +that’s fine. You process should now detect that it is the only one +remaining in the group. Now is the right time to collect all the +metrics you need! + +Finally, your process should move itself back to the root control +group, and remove the container control group. To remove a control +group, just ``rmdir`` its directory. It's counter-intuitive to +``rmdir`` a directory as it still contains files; but remember that +this is a pseudo-filesystem, so usual rules don't apply. After the +cleanup is done, the collection process can exit safely. + diff --git a/components/engine/docs/sources/reference/builder.rst b/components/engine/docs/sources/reference/builder.rst index 45cb2ab86e..9889660913 100644 --- a/components/engine/docs/sources/reference/builder.rst +++ b/components/engine/docs/sources/reference/builder.rst @@ -1,12 +1,12 @@ -:title: Build Images (Dockerfile Reference) +:title: Dockerfile Reference :description: Dockerfiles use a simple DSL which allows you to automate the steps you would normally manually take to create an image. :keywords: builder, docker, Dockerfile, automation, image creation .. _dockerbuilder: -=================================== -Build Images (Dockerfile Reference) -=================================== +==================== +Dockerfile Reference +==================== **Docker can act as a builder** and read instructions from a text ``Dockerfile`` to automate the steps you would otherwise take manually diff --git a/components/engine/docs/sources/reference/commandline/cli.rst b/components/engine/docs/sources/reference/commandline/cli.rst index e71b691bcc..a636df6259 100644 --- a/components/engine/docs/sources/reference/commandline/cli.rst +++ b/components/engine/docs/sources/reference/commandline/cli.rst @@ -18,6 +18,45 @@ To list available commands, either run ``docker`` with no parameters or execute ... +.. _cli_options: + +Types of Options +---------------- + +Boolean +~~~~~~~ + +Boolean options look like ``-d=false``. The value you see is the +default value which gets set if you do **not** use the boolean +flag. If you do call ``run -d``, that sets the opposite boolean value, +so in this case, ``true``, and so ``docker run -d`` **will** run in +"detached" mode, in the background. Other boolean options are similar +-- specifying them will set the value to the opposite of the default +value. + +Multi +~~~~~ + +Options like ``-a=[]`` indicate they can be specified multiple times:: + + docker run -a stdin -a stdout -a stderr -i -t ubuntu /bin/bash + +Sometimes this can use a more complex value string, as for ``-v``:: + + docker run -v /host:/container example/mysql + +Strings and Integers +~~~~~~~~~~~~~~~~~~~~ + +Options like ``-name=""`` expect a string, and they can only be +specified once. Options like ``-c=0`` expect an integer, and they can +only be specified once. + +---- + +Commands +-------- + .. _cli_daemon: ``daemon`` diff --git a/components/engine/docs/sources/reference/index.rst b/components/engine/docs/sources/reference/index.rst index 49099d5621..d35a19b93d 100644 --- a/components/engine/docs/sources/reference/index.rst +++ b/components/engine/docs/sources/reference/index.rst @@ -14,4 +14,5 @@ Contents: commandline/index builder + run api/index diff --git a/components/engine/docs/sources/reference/run.rst b/components/engine/docs/sources/reference/run.rst new file mode 100644 index 0000000000..7505b7c02f --- /dev/null +++ b/components/engine/docs/sources/reference/run.rst @@ -0,0 +1,353 @@ +:title: Docker Run Reference +:description: Configure containers at runtime +:keywords: docker, run, configure, runtime + +.. _run_docker: + +==================== +Docker Run Reference +==================== + +**Docker runs processes in isolated containers**. When an operator +executes ``docker run``, she starts a process with its own file +system, its own networking, and its own isolated process tree. The +:ref:`image_def` which starts the process may define defaults related +to the binary to run, the networking to expose, and more, but ``docker +run`` gives final control to the operator who starts the container +from the image. That's the main reason :ref:`cli_run` has more options +than any other ``docker`` command. + +Every one of the :ref:`example_list` shows running containers, and so +here we try to give more in-depth guidance. + +.. contents:: Table of Contents + +.. _run_running: + +General Form +============ + +As you've seen in the :ref:`example_list`, the basic `run` command +takes this form:: + + docker run [OPTIONS] IMAGE[:TAG] [COMMAND] [ARG...] + +To learn how to interpret the types of ``[OPTIONS]``, see +:ref:`cli_options`. + +The list of ``[OPTIONS]`` breaks down into two groups: + +* options that define the runtime behavior or environment, and +* options that override image defaults. + +Since image defaults usually get set in :ref:`Dockerfiles +` (though they could also be set at :ref:`cli_commit` +time too), we will group the runtime options here by their related +Dockerfile commands so that it is easier to see how to override image +defaults and set new behavior. + +We'll start, though, with the options that are unique to ``docker +run``, the options which define the runtime behavior or the container +environment. + +.. note:: The runtime operator always has final control over the + behavior of a Docker container. + +Detached or Foreground +====================== + +When starting a Docker container, you must first decide if you want to +run the container in the background in a "detached" mode or in the +default foreground mode:: + + -d=false: Detached mode: Run container in the background, print new container id + +Detached (-d) +............. + +In detached mode (``-d=true`` or just ``-d``), all IO should be done +through network connections or shared volumes because the container is +no longer listening to the commandline where you executed ``docker +run``. You can reattach to a detached container with ``docker`` +:ref:`cli_attach`. If you choose to run a container in the detached +mode, then you cannot use the ``-rm`` option. + +Foreground +.......... + +In foreground mode (the default when ``-d`` is not specified), +``docker run`` can start the process in the container and attach the +console to the process's standard input, output, and standard +error. It can even pretend to be a TTY (this is what most commandline +executables expect) and pass along signals. All of that is +configurable:: + + -a=[] : Attach to stdin, stdout and/or stderr + -t=false : Allocate a pseudo-tty + -sig-proxy=true: Proxify all received signal to the process (even in non-tty mode) + -i=false : Keep stdin open even if not attached + +If you do not specify ``-a`` then Docker will `attach everything +(stdin,stdout,stderr) +`_. You +can specify which of the three standard streams (stdin, stdout, +stderr) you'd like to connect between your instead, as in:: + + docker run -a stdin -a stdout -i -t ubuntu /bin/bash + +For interactive processes (like a shell) you will typically want a tty +as well as persistent standard in, so you'll use ``-i -t`` together in +most interactive cases. + +Clean Up (-rm) +-------------- + +By default a container's file system persists even after the container +exits. This makes debugging a lot easier (since you can inspect the +final state) and you retain all your data by default. But if you are +running short-term **foreground** processes, these container file +systems can really pile up. If instead you'd like Docker to +**automatically clean up the container and remove the file system when +the container exits**, you can add the ``-rm`` flag:: + + -rm=false: Automatically remove the container when it exits (incompatible with -d) + +Name (-name) +============ + +The operator can identify a container in three ways: + +* UUID long identifier ("f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778") +* UUID short identifier ("f78375b1c487") +* name ("evil_ptolemy") + +The UUID identifiers come from the Docker daemon, and if you do not +assign a name to the container with ``-name`` then the daemon will +also generate a random string name too. The name can become a handy +way to add meaning to a container since you can use this name when +defining :ref:`links ` (or any other place +you need to identify a container). This works for both background and +foreground Docker containers. + +PID Equivalent +============== + +And finally, to help with automation, you can have Docker write the +container id out to a file of your choosing. This is similar to how +some programs might write out their process ID to a file (you've seen +them as .pid files):: + + -cidfile="": Write the container ID to the file + +Overriding Dockerfile Image Defaults +==================================== + +When a developer builds an image from a :ref:`Dockerfile +` or when she commits it, the developer can set a +number of default parameters that take effect when the image starts up +as a container. + +Four of the Dockerfile commands cannot be overridden at runtime: +``FROM, MAINTAINER, RUN``, and ``ADD``. Everything else has a +corresponding override in ``docker run``. We'll go through what the +developer might have set in each Dockerfile instruction and how the +operator can override that setting. + + +CMD +... + +Remember the optional ``COMMAND`` in the Docker commandline:: + + docker run [OPTIONS] IMAGE[:TAG] [COMMAND] [ARG...] + +This command is optional because the person who created the ``IMAGE`` +may have already provided a default ``COMMAND`` using the Dockerfile +``CMD``. As the operator (the person running a container from the +image), you can override that ``CMD`` just by specifying a new +``COMMAND``. + +If the image also specifies an ``ENTRYPOINT`` then the ``CMD`` or +``COMMAND`` get appended as arguments to the ``ENTRYPOINT``. + + +ENTRYPOINT +.......... + +:: + + -entrypoint="": Overwrite the default entrypoint set by the image + +The ENTRYPOINT of an image is similar to a COMMAND because it +specifies what executable to run when the container starts, but it is +(purposely) more difficult to override. The ENTRYPOINT gives a +container its default nature or behavior, so that when you set an +ENTRYPOINT you can run the container *as if it were that binary*, +complete with default options, and you can pass in more options via +the COMMAND. But, sometimes an operator may want to run something else +inside the container, so you can override the default ENTRYPOINT at +runtime by using a string to specify the new ENTRYPOINT. Here is an +example of how to run a shell in a container that has been set up to +automatically run something else (like ``/usr/bin/redis-server``):: + + docker run -i -t -entrypoint /bin/bash example/redis + +or two examples of how to pass more parameters to that ENTRYPOINT:: + + docker run -i -t -entrypoint /bin/bash example/redis -c ls -l + docker run -i -t -entrypoint /usr/bin/redis-cli example/redis --help + + +EXPOSE (``run`` Networking Options) +................................... + +The *Dockerfile* doesn't give much control over networking, only +providing the EXPOSE instruction to give a hint to the operator about +what incoming ports might provide services. At runtime, however, +Docker provides a number of ``run`` options related to networking:: + + -n=true : Enable networking for this container + -dns=[] : Set custom dns servers for the container + -expose=[]: Expose a port from the container + without publishing it to your host + -P=false : Publish all exposed ports to the host interfaces + -p=[] : Publish a container's port to the host (format: + ip:hostPort:containerPort | ip::containerPort | + hostPort:containerPort) + (use 'docker port' to see the actual mapping) + -link="" : Add link to another container (name:alias) + +By default, all containers have networking enabled and they can make +any outgoing connections. The operator can completely disable +networking with ``run -n`` which disables all incoming and outgoing +networking. In cases like this, you would perform IO through files or +stdin/stdout only. + +Your container will use the same DNS servers as the host by default, +but you can override this with ``-dns``. + +As mentioned previously, ``EXPOSE`` (and ``-expose``) make a port +available **in** a container for incoming connections. The port number +on the inside of the container (where the service listens) does not +need to be the same number as the port exposed on the outside of the +container (where clients connect), so inside the container you might +have an HTTP service listening on port 80 (and so you ``EXPOSE 80`` in +the Dockerfile), but outside the container the port might be 42800. + +To help a new client container reach the server container's internal +port operator ``-expose'd`` by the operator or ``EXPOSE'd`` by the +developer, the operator has three choices: start the server container +with ``-P`` or ``-p,`` or start the client container with ``-link``. + +If the operator uses ``-P`` or ``-p`` then Docker will make the +exposed port accessible on the host and the ports will be available to +any client that can reach the host. To find the map between the host +ports and the exposed ports, use ``docker port``) + +If the operator uses ``-link`` when starting the new client container, +then the client container can access the exposed port via a private +networking interface. Docker will set some environment variables in +the client container to help indicate which interface and port to use. + +ENV (Environment Variables) +........................... + +The operator can **set any environment variable** in the container by +using one or more ``-e``, even overriding those already defined by the +developer with a Dockefile ``ENV``:: + + $ docker run -e "deep=purple" -rm ubuntu /bin/bash -c export + declare -x HOME="/" + declare -x HOSTNAME="85bc26a0e200" + declare -x OLDPWD + declare -x PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" + declare -x PWD="/" + declare -x SHLVL="1" + declare -x container="lxc" + declare -x deep="purple" + +Similarly the operator can set the **hostname** with ``-h``. + +``-link name:alias`` also sets environment variables, using the +*alias* string to define environment variables within the container +that give the IP and PORT information for connecting to the service +container. Let's imagine we have a container running Redis:: + + # Start the service container, named redis-name + $ docker run -d -name redis-name dockerfiles/redis + 4241164edf6f5aca5b0e9e4c9eccd899b0b8080c64c0cd26efe02166c73208f3 + + # The redis-name container exposed port 6379 + $ docker ps + CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES + 4241164edf6f dockerfiles/redis:latest /redis-stable/src/re 5 seconds ago Up 4 seconds 6379/tcp redis-name + + # Note that there are no public ports exposed since we didn't use -p or -P + $ docker port 4241164edf6f 6379 + 2014/01/25 00:55:38 Error: No public port '6379' published for 4241164edf6f + + +Yet we can get information about the redis container's exposed ports with ``-link``. Choose an alias that will form a valid environment variable! + +:: + + $ docker run -rm -link redis-name:redis_alias -entrypoint /bin/bash dockerfiles/redis -c export + declare -x HOME="/" + declare -x HOSTNAME="acda7f7b1cdc" + declare -x OLDPWD + declare -x PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" + declare -x PWD="/" + declare -x REDIS_ALIAS_NAME="/distracted_wright/redis" + declare -x REDIS_ALIAS_PORT="tcp://172.17.0.32:6379" + declare -x REDIS_ALIAS_PORT_6379_TCP="tcp://172.17.0.32:6379" + declare -x REDIS_ALIAS_PORT_6379_TCP_ADDR="172.17.0.32" + declare -x REDIS_ALIAS_PORT_6379_TCP_PORT="6379" + declare -x REDIS_ALIAS_PORT_6379_TCP_PROTO="tcp" + declare -x SHLVL="1" + declare -x container="lxc" + +And we can use that information to connect from another container as a client:: + + $ docker run -i -t -rm -link redis-name:redis_alias -entrypoint /bin/bash dockerfiles/redis -c '/redis-stable/src/redis-cli -h $REDIS_ALIAS_PORT_6379_TCP_ADDR -p $REDIS_ALIAS_PORT_6379_TCP_PORT' + 172.17.0.32:6379> + +VOLUME (Shared Filesystems) +........................... + +:: + + -v=[]: Create a bind mount with: [host-dir]:[container-dir]:[rw|ro]. + If "container-dir" is missing, then docker creates a new volume. + -volumes-from="": Mount all volumes from the given container(s) + +The volumes commands are complex enough to have their own +documentation in section :ref:`volume_def`. A developer can define one +or more VOLUMEs associated with an image, but only the operator can +give access from one container to another (or from a container to a +volume mounted on the host). + +USER +.... + +:: + + -u="": Username or UID + +WORKDIR +....... + +:: + + -w="": Working directory inside the container + +Performance +=========== + +The operator can also adjust the performance parameters of the container:: + + -c=0 : CPU shares (relative weight) + -m="": Memory limit (format: , where unit = b, k, m or g) + + -lxc-conf=[]: Add custom lxc options -lxc-conf="lxc.cgroup.cpuset.cpus = 0,1" + -privileged=false: Give extended privileges to this container + From ec0c7b984233e51a8a8a5cb113aafb29467d9a4a Mon Sep 17 00:00:00 2001 From: Andy Rothfusz Date: Tue, 28 Jan 2014 17:32:05 -0800 Subject: [PATCH 2/2] Address feedback from @jamtur01. Docker-DCO-1.1-Signed-off-by: Andy Rothfusz (github: metalivedev) Upstream-commit: f3a032f27b80e8194cb7f14df848f063a56c5f26 Component: engine --- .../docs/sources/articles/runmetrics.rst | 26 +- .../engine/docs/sources/reference/run.rst | 260 +++++++++++------- 2 files changed, 173 insertions(+), 113 deletions(-) diff --git a/components/engine/docs/sources/articles/runmetrics.rst b/components/engine/docs/sources/articles/runmetrics.rst index f7406bc5ed..afb7f82e39 100644 --- a/components/engine/docs/sources/articles/runmetrics.rst +++ b/components/engine/docs/sources/articles/runmetrics.rst @@ -37,8 +37,8 @@ To figure out where your control groups are mounted, you can run: .. _run_findpid: -Ennumerating Cgroups --------------------- +Enumerating Cgroups +------------------- You can look into ``/proc/cgroups`` to see the different control group subsystems known to the system, the hierarchy they belong to, and how @@ -71,7 +71,7 @@ container, take a look at ``/sys/fs/cgroup/memory/lxc//``. Metrics from Cgroups: Memory, CPU, Block IO ------------------------------------------- -For each subsystem (memory, cpu, and block i/o), you will find one or +For each subsystem (memory, CPU, and block I/O), you will find one or more pseudo-files containing statistics. Memory Metrics: ``memory.stat`` @@ -79,7 +79,7 @@ Memory Metrics: ``memory.stat`` Memory metrics are found in the "memory" cgroup. Note that the memory control group adds a little overhead, because it does very -fine-grained accounting of the memory usage on your system. Therefore, +fine-grained accounting of the memory usage on your host. Therefore, many distros chose to not enable it by default. Generally, to enable it, all you have to do is to add some kernel command-line parameters: ``cgroup_enable=memory swapaccount=1``. @@ -133,7 +133,7 @@ creation of the cgroup; this number can never decrease). cache the amount of memory used by the processes of this control group that can be associated precisely with a block on a block - device. When you read and write files from and to disk, this amount + device. When you read from and write to files on disk, this amount will increase. This will be the case if you use "conventional" I/O (``open``, ``read``, ``write`` syscalls) as well as mapped files (with ``mmap``). It also accounts for the memory used by ``tmpfs`` @@ -148,17 +148,11 @@ mapped_file control group. It doesn't give you information about *how much* memory is used; it rather tells you *how* it is used. -pgpgin and pgpgout - correspond to *charging events*. Each time a page is "charged" - (=added to the accounting) to a cgroup, pgpgin increases. When a - page is "uncharged" (=no longer "billed" to a cgroup), pgpgout - increases. - pgfault and pgmajfault indicate the number of times that a process of the cgroup triggered a "page fault" and a "major fault", respectively. A page fault happens when a process accesses a part of its virtual memory space - which is inexistent or protected. The former can happen if the + which is nonexistent or protected. The former can happen if the process is buggy and tries to access an invalid address (it will then be sent a ``SIGSEGV`` signal, typically killing it with the famous ``Segmentation fault`` message). The latter can happen when @@ -237,7 +231,7 @@ the processes were in direct control of the CPU (i.e. executing process code), and ``system`` is the time during which the CPU was executing system calls on behalf of those processes. -Those times are expressed in ticks of 1/100th of second. Actually, +Those times are expressed in ticks of 1/100th of a second. Actually, they are expressed in "user jiffies". There are ``USER_HZ`` *"jiffies"* per second, and on x86 systems, ``USER_HZ`` is 100. This used to map exactly to the number of scheduler "ticks" per second; but @@ -383,11 +377,11 @@ pseudo-files. (Symlinks are accepted.) In other words, to execute a command within the network namespace of a container, we need to: -* find out the PID of any process within the container that we want to +* Find out the PID of any process within the container that we want to investigate; -* create a symlink from ``/var/run/netns/`` to +* Create a symlink from ``/var/run/netns/`` to ``/proc//ns/net`` -* execute ``ip netns exec ....`` +* Execute ``ip netns exec ....`` Please review :ref:`run_findpid` to learn how to find the cgroup of a pprocess running in the container of which you want to measure network diff --git a/components/engine/docs/sources/reference/run.rst b/components/engine/docs/sources/reference/run.rst index 7505b7c02f..307edace00 100644 --- a/components/engine/docs/sources/reference/run.rst +++ b/components/engine/docs/sources/reference/run.rst @@ -21,6 +21,7 @@ Every one of the :ref:`example_list` shows running containers, and so here we try to give more in-depth guidance. .. contents:: Table of Contents + :depth: 2 .. _run_running: @@ -37,24 +38,33 @@ To learn how to interpret the types of ``[OPTIONS]``, see The list of ``[OPTIONS]`` breaks down into two groups: -* options that define the runtime behavior or environment, and -* options that override image defaults. +1. Settings exclusive to operators, including: -Since image defaults usually get set in :ref:`Dockerfiles -` (though they could also be set at :ref:`cli_commit` -time too), we will group the runtime options here by their related -Dockerfile commands so that it is easier to see how to override image -defaults and set new behavior. + * Detached or Foreground running, + * Container Identification, + * Network settings, and + * Runtime Constraints on CPU and Memory + * Privileges and LXC Configuration -We'll start, though, with the options that are unique to ``docker -run``, the options which define the runtime behavior or the container -environment. +2. Setting shared between operators and developers, where operators + can override defaults developers set in images at build time. -.. note:: The runtime operator always has final control over the - behavior of a Docker container. +Together, the ``docker run [OPTIONS]`` give complete control over +runtime behavior to the operator, allowing them to override all +defaults set by the developer during ``docker build`` and nearly all +the defaults set by the Docker runtime itself. -Detached or Foreground -====================== +Operator Exclusive Options +========================== + +Only the operator (the person executing ``docker run``) can set the +following options. + +.. contents:: + :local: + +Detached vs Foreground +---------------------- When starting a Docker container, you must first decide if you want to run the container in the background in a "detached" mode or in the @@ -65,7 +75,7 @@ default foreground mode:: Detached (-d) ............. -In detached mode (``-d=true`` or just ``-d``), all IO should be done +In detached mode (``-d=true`` or just ``-d``), all I/O should be done through network connections or shared volumes because the container is no longer listening to the commandline where you executed ``docker run``. You can reattach to a detached container with ``docker`` @@ -82,22 +92,68 @@ error. It can even pretend to be a TTY (this is what most commandline executables expect) and pass along signals. All of that is configurable:: - -a=[] : Attach to stdin, stdout and/or stderr + -a=[] : Attach to ``stdin``, ``stdout`` and/or ``stderr`` -t=false : Allocate a pseudo-tty -sig-proxy=true: Proxify all received signal to the process (even in non-tty mode) - -i=false : Keep stdin open even if not attached + -i=false : Keep STDIN open even if not attached If you do not specify ``-a`` then Docker will `attach everything (stdin,stdout,stderr) -`_. You -can specify which of the three standard streams (stdin, stdout, -stderr) you'd like to connect between your instead, as in:: +`_. You +can specify to which of the three standard streams (``stdin``, ``stdout``, +``stderr``) you'd like to connect instead, as in:: docker run -a stdin -a stdout -i -t ubuntu /bin/bash For interactive processes (like a shell) you will typically want a tty -as well as persistent standard in, so you'll use ``-i -t`` together in -most interactive cases. +as well as persistent standard input (``stdin``), so you'll use ``-i +-t`` together in most interactive cases. + +Container Identification +------------------------ + +Name (-name) +............ + +The operator can identify a container in three ways: + +* UUID long identifier ("f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778") +* UUID short identifier ("f78375b1c487") +* Name ("evil_ptolemy") + +The UUID identifiers come from the Docker daemon, and if you do not +assign a name to the container with ``-name`` then the daemon will +also generate a random string name too. The name can become a handy +way to add meaning to a container since you can use this name when +defining :ref:`links ` (or any other place +you need to identify a container). This works for both background and +foreground Docker containers. + +PID Equivalent +.............. + +And finally, to help with automation, you can have Docker write the +container ID out to a file of your choosing. This is similar to how +some programs might write out their process ID to a file (you've seen +them as PID files):: + + -cidfile="": Write the container ID to the file + +Network Settings +---------------- + +:: + -n=true : Enable networking for this container + -dns=[] : Set custom dns servers for the container + +By default, all containers have networking enabled and they can make +any outgoing connections. The operator can completely disable +networking with ``docker run -n`` which disables all incoming and outgoing +networking. In cases like this, you would perform I/O through files or +STDIN/STDOUT only. + +Your container will use the same DNS servers as the host by default, +but you can override this with ``-dns``. Clean Up (-rm) -------------- @@ -112,57 +168,84 @@ the container exits**, you can add the ``-rm`` flag:: -rm=false: Automatically remove the container when it exits (incompatible with -d) -Name (-name) -============ -The operator can identify a container in three ways: +Runtime Constraints on CPU and Memory +------------------------------------- -* UUID long identifier ("f78375b1c487e03c9438c729345e54db9d20cfa2ac1fc3494b6eb60872e74778") -* UUID short identifier ("f78375b1c487") -* name ("evil_ptolemy") +The operator can also adjust the performance parameters of the container:: -The UUID identifiers come from the Docker daemon, and if you do not -assign a name to the container with ``-name`` then the daemon will -also generate a random string name too. The name can become a handy -way to add meaning to a container since you can use this name when -defining :ref:`links ` (or any other place -you need to identify a container). This works for both background and -foreground Docker containers. + -m="": Memory limit (format: , where unit = b, k, m or g) + -c=0 : CPU shares (relative weight) -PID Equivalent -============== +The operator can constrain the memory available to a container easily +with ``docker run -m``. If the host supports swap memory, then the +``-m`` memory setting can be larger than physical RAM. -And finally, to help with automation, you can have Docker write the -container id out to a file of your choosing. This is similar to how -some programs might write out their process ID to a file (you've seen -them as .pid files):: +Similarly the operator can increase the priority of this container +with the ``-c`` option. By default, all containers run at the same +priority and get the same proportion of CPU cycles, but you can tell +the kernel to give more shares of CPU time to one or more containers +when you start them via Docker. - -cidfile="": Write the container ID to the file +Runtime Privilege and LXC Configuration +--------------------------------------- -Overriding Dockerfile Image Defaults -==================================== +:: + + -privileged=false: Give extended privileges to this container + -lxc-conf=[]: Add custom lxc options -lxc-conf="lxc.cgroup.cpuset.cpus = 0,1" + +By default, Docker containers are "unprivileged" and cannot, for +example, run a Docker daemon inside a Docker container. This is +because by default a container is not allowed to access any devices, +but a "privileged" container is given access to all devices (see +lxc-template.go_ and documentation on `cgroups devices +`_). + +When the operator executes ``docker run -privileged``, Docker will +enable to access to all devices on the host as well as set some +configuration in AppArmor to allow the container nearly all the same +access to the host as processes running outside containers on the +host. Additional information about running with ``-privileged`` is +available on the `Docker Blog +`_. + +An operator can also specify LXC options using one or more +``-lxc-conf`` parameters. These can be new parameters or override +existing parameters from the lxc-template.go_. Note that in the +future, a given host's Docker daemon may not use LXC, so this is an +implementation-specific configuration meant for operators already +familiar with using LXC directly. + +.. _lxc-template.go: https://github.com/dotcloud/docker/blob/master/execdriver/lxc/lxc_template.go + + +Overriding ``Dockerfile`` Image Defaults +======================================== When a developer builds an image from a :ref:`Dockerfile ` or when she commits it, the developer can set a number of default parameters that take effect when the image starts up as a container. -Four of the Dockerfile commands cannot be overridden at runtime: +Four of the ``Dockerfile`` commands cannot be overridden at runtime: ``FROM, MAINTAINER, RUN``, and ``ADD``. Everything else has a corresponding override in ``docker run``. We'll go through what the -developer might have set in each Dockerfile instruction and how the +developer might have set in each ``Dockerfile`` instruction and how the operator can override that setting. +.. contents:: + :local: -CMD -... +CMD (Default Command or Options) +-------------------------------- -Remember the optional ``COMMAND`` in the Docker commandline:: +Recall the optional ``COMMAND`` in the Docker commandline:: docker run [OPTIONS] IMAGE[:TAG] [COMMAND] [ARG...] This command is optional because the person who created the ``IMAGE`` -may have already provided a default ``COMMAND`` using the Dockerfile +may have already provided a default ``COMMAND`` using the ``Dockerfile`` ``CMD``. As the operator (the person running a container from the image), you can override that ``CMD`` just by specifying a new ``COMMAND``. @@ -171,22 +254,22 @@ If the image also specifies an ``ENTRYPOINT`` then the ``CMD`` or ``COMMAND`` get appended as arguments to the ``ENTRYPOINT``. -ENTRYPOINT -.......... +ENTRYPOINT (Default Command to Execute at Runtime +------------------------------------------------- :: -entrypoint="": Overwrite the default entrypoint set by the image -The ENTRYPOINT of an image is similar to a COMMAND because it +The ENTRYPOINT of an image is similar to a ``COMMAND`` because it specifies what executable to run when the container starts, but it is -(purposely) more difficult to override. The ENTRYPOINT gives a +(purposely) more difficult to override. The ``ENTRYPOINT`` gives a container its default nature or behavior, so that when you set an -ENTRYPOINT you can run the container *as if it were that binary*, +``ENTRYPOINT`` you can run the container *as if it were that binary*, complete with default options, and you can pass in more options via -the COMMAND. But, sometimes an operator may want to run something else -inside the container, so you can override the default ENTRYPOINT at -runtime by using a string to specify the new ENTRYPOINT. Here is an +the ``COMMAND``. But, sometimes an operator may want to run something else +inside the container, so you can override the default ``ENTRYPOINT`` at +runtime by using a string to specify the new ``ENTRYPOINT``. Here is an example of how to run a shell in a container that has been set up to automatically run something else (like ``/usr/bin/redis-server``):: @@ -198,16 +281,14 @@ or two examples of how to pass more parameters to that ENTRYPOINT:: docker run -i -t -entrypoint /usr/bin/redis-cli example/redis --help -EXPOSE (``run`` Networking Options) -................................... +EXPOSE (Incoming Ports) +----------------------- -The *Dockerfile* doesn't give much control over networking, only -providing the EXPOSE instruction to give a hint to the operator about -what incoming ports might provide services. At runtime, however, -Docker provides a number of ``run`` options related to networking:: +The ``Dockerfile`` doesn't give much control over networking, only +providing the ``EXPOSE`` instruction to give a hint to the operator +about what incoming ports might provide services. The following +options work with or override the ``Dockerfile``'s exposed defaults:: - -n=true : Enable networking for this container - -dns=[] : Set custom dns servers for the container -expose=[]: Expose a port from the container without publishing it to your host -P=false : Publish all exposed ports to the host interfaces @@ -217,25 +298,16 @@ Docker provides a number of ``run`` options related to networking:: (use 'docker port' to see the actual mapping) -link="" : Add link to another container (name:alias) -By default, all containers have networking enabled and they can make -any outgoing connections. The operator can completely disable -networking with ``run -n`` which disables all incoming and outgoing -networking. In cases like this, you would perform IO through files or -stdin/stdout only. - -Your container will use the same DNS servers as the host by default, -but you can override this with ``-dns``. - As mentioned previously, ``EXPOSE`` (and ``-expose``) make a port available **in** a container for incoming connections. The port number on the inside of the container (where the service listens) does not need to be the same number as the port exposed on the outside of the container (where clients connect), so inside the container you might have an HTTP service listening on port 80 (and so you ``EXPOSE 80`` in -the Dockerfile), but outside the container the port might be 42800. +the ``Dockerfile``), but outside the container the port might be 42800. To help a new client container reach the server container's internal -port operator ``-expose'd`` by the operator or ``EXPOSE'd`` by the +port operator ``-expose``'d by the operator or ``EXPOSE``'d by the developer, the operator has three choices: start the server container with ``-P`` or ``-p,`` or start the client container with ``-link``. @@ -250,10 +322,10 @@ networking interface. Docker will set some environment variables in the client container to help indicate which interface and port to use. ENV (Environment Variables) -........................... +--------------------------- The operator can **set any environment variable** in the container by -using one or more ``-e``, even overriding those already defined by the +using one or more ``-e`` flags, even overriding those already defined by the developer with a Dockefile ``ENV``:: $ docker run -e "deep=purple" -rm ubuntu /bin/bash -c export @@ -287,7 +359,9 @@ container. Let's imagine we have a container running Redis:: 2014/01/25 00:55:38 Error: No public port '6379' published for 4241164edf6f -Yet we can get information about the redis container's exposed ports with ``-link``. Choose an alias that will form a valid environment variable! +Yet we can get information about the Redis container's exposed ports +with ``-link``. Choose an alias that will form a valid environment +variable! :: @@ -312,7 +386,7 @@ And we can use that information to connect from another container as a client:: 172.17.0.32:6379> VOLUME (Shared Filesystems) -........................... +--------------------------- :: @@ -322,32 +396,24 @@ VOLUME (Shared Filesystems) The volumes commands are complex enough to have their own documentation in section :ref:`volume_def`. A developer can define one -or more VOLUMEs associated with an image, but only the operator can +or more ``VOLUME``\s associated with an image, but only the operator can give access from one container to another (or from a container to a volume mounted on the host). USER -.... +---- -:: +The default user within a container is ``root`` (id = 0), but if the +developer created additional users, those are accessible too. The +developer can set a default user to run the first process with the +``Dockerfile USER`` command, but the operator can override it :: -u="": Username or UID WORKDIR -....... +------- -:: +The default working directory for running binaries within a container is the root directory (``/``), but the developer can set a different default with the ``Dockerfile WORKDIR`` command. The operator can override this with:: -w="": Working directory inside the container -Performance -=========== - -The operator can also adjust the performance parameters of the container:: - - -c=0 : CPU shares (relative weight) - -m="": Memory limit (format: , where unit = b, k, m or g) - - -lxc-conf=[]: Add custom lxc options -lxc-conf="lxc.cgroup.cpuset.cpus = 0,1" - -privileged=false: Give extended privileges to this container -