Add tag support to journald logging driver, closes #19556

Signed-off-by: Ivan Babrou <ibobrik@gmail.com>
Upstream-commit: 5a3351883b254d3690e9dcc5b89293bcee474493
Component: engine

components/engine/docs/admin/logging/journald.md

@@ -24,6 +24,7 @@ driver stores the following metadata in the journal with each message:
 | `CONTAINER_ID`      | The container ID truncated to 12 characters. |
 | `CONTAINER_ID_FULL` | The full 64-character container ID. |
 | `CONTAINER_NAME`    | The container name at the time it was started. If you use `docker rename` to rename a container, the new name is not reflected in the journal entries. |
+| `CONTAINER_TAG`     | The container tag ([log tag option documentation](log_tags.md)). |
 
 ## Usage
 
@@ -42,6 +43,11 @@ You can set the logging driver for a specific container by using the
 Users can use the `--log-opt NAME=VALUE` flag to specify additional
 journald logging driver options.
 
+### tag
+
+Specify template to set `CONTAINER_TAG` value in journald logs. Refer to
+[log tag option documentation](log_tags.md) for customizing the log tag format.
+
 ### labels and env
 
 The `labels` and `env` options each take a comma-separated list of keys. If there is collision between `label` and `env` keys, the value of the `env` takes precedence. Both options add additional metadata in the journal with each message.

components/engine/docs/admin/logging/log_tags.md

@@ -3,7 +3,7 @@
 aliases = ["/engine/reference/logging/log_tags/"]
 title = "Log tags for logging driver"
 description = "Describes how to format tags for."
-keywords = ["docker, logging, driver, syslog, Fluentd, gelf"]
+keywords = ["docker, logging, driver, syslog, Fluentd, gelf, journald"]
 [menu.main]
 parent = "smn_logging"
 weight = 1