docker-cli/components/engine/docs/swarm/swarm-tutorial/rolling-update.md

Apply rolling updates to a service

In a previous step of the tutorial, you scaled the number of instances of a service. In this part of the tutorial, you deploy a new Redis service and upgrade the service using rolling updates.

1. If you haven't already, open a terminal and ssh into the machine where you run your manager node. For example, the tutorial uses a machine named manager1.

2. Deploy Redis 3.0.6 to all nodes in the Swarm and configure the swarm to update one node every 10 seconds:

   $ docker service create --replicas 3 --name redis --update-delay 10s --update-parallelism 1 redis:3.0.6
   
   8m228injfrhdym2zvzhl9k3l0
   

   You configure the rolling update policy at service deployment time.

   The --update-parallelism flag configures the number of service tasks to update simultaneously.

   The --update-delay flag configures the time delay between updates to a service task or sets of tasks. You can describe the time T as a combination of the number of seconds Ts, minutes Tm, or hours Th. So 10m30s indicates a 10 minute 30 second delay.

3. Inspect the redis service:

   $ docker service inspect redis --pretty
   
   ID:		75kcmhuf8mif4a07738wttmgl
   Name:		redis
   Mode:		REPLICATED
    Scale:	3
   Placement:
    Strategy:	SPREAD
   UpdateConfig:
    Parallelism:	1
    Delay:		10s
   ContainerSpec:
    Image:		redis:3.0.6
   

4. Now you can update the container image for redis. Swarm applies the update to nodes according to the UpdateConfig policy:

   $ docker service update --image redis:3.0.7 redis
   redis
   

5. Run docker service inspect --pretty redis to see the new image in the desired state:

   docker service inspect --pretty redis
   
   ID:		1yrcci9v8zj6cokua2eishlob
   Name:		redis
   Mode:		REPLICATED
    Scale:		3
   Placement:
    Strategy:	SPREAD
   UpdateConfig:
    Parallelism:	1
    Delay:		10s
   ContainerSpec:
   Image:		redis:3.0.7
   

6. Run docker service tasks <TASK-ID> to watch the rolling update:

   $ docker service tasks redis
   
   ID                         NAME     SERVICE  IMAGE        DESIRED STATE  LAST STATE          NODE
   5409nu4crb0smamziqwuug67u  redis.1  redis    redis:3.0.7  RUNNING        RUNNING 21 seconds  worker2
   b8ezq58zugcg1trk8k7jrq9ym  redis.2  redis    redis:3.0.7  RUNNING        RUNNING 1 seconds   worker1
   cgdcbipxnzx0y841vysiafb64  redis.3  redis    redis:3.0.7  RUNNING        RUNNING 11 seconds  worker1
   

   Before Swarm updates all of the tasks, you can see that some are running redis:3.0.6 while others are running redis:3.0.7. The output above shows the state once the rolling updates are done. You can see that each instances entered the RUNNING state in 10 second increments.

Next, learn about how to drain a node in the Swarm.