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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 service based on the Redis 3.0.6 container image. Then you upgrade the service to use the Redis 3.0.7 container image 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 the swarm and configure the swarm with a 10 second update delay:

    $ docker service create \
      --replicas 3 \
      --name redis \
      --update-delay 10s \
      redis:3.0.6
    
    0u6a4s31ybk7yw2wyvtikmu50
    

    You configure the rolling update policy at service deployment time.

    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.

    By default the scheduler updates 1 task at a time. You can pass the --update-parallelism flag to configure the maximum number of service tasks that the scheduler updates simultaneously.

    By default, when an update to an individual task returns a state of RUNNING, the scheduler schedules another task to update until all tasks are updated. If, at any time during an update a task returns FAILED, the scheduler pauses the update. You can control the behavior using the --update-failure-action flag for docker service create or docker service update.

  3. Inspect the redis service:

    $ docker service inspect --pretty redis
    
    ID:             0u6a4s31ybk7yw2wyvtikmu50
    Name:           redis
    Mode:           Replicated
     Replicas:      3
    Placement:
     Strategy:      Spread
    UpdateConfig:
     Parallelism:   1
     Delay:         10s
    ContainerSpec:
     Image:         redis:3.0.6
    Resources:
    
  4. Now you can update the container image for redis. The swarm manager applies the update to nodes according to the UpdateConfig policy:

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

    The scheduler applies rolling updates as follows by default:

    • Stop the first task.
    • Schedule update for the stopped task.
    • Start the container for the updated task.
    • If the update to a task returns RUNNING, wait for the specified delay period then stop the next task.
    • If, at any time during the update, a task returns FAILED, pause the update.
  5. Run docker service inspect --pretty redis to see the new image in the desired state:

    $ docker service inspect --pretty redis
    
    ID:             0u6a4s31ybk7yw2wyvtikmu50
    Name:           redis
    Mode:           Replicated
     Replicas:      3
    Placement:
     Strategy:      Spread
    UpdateConfig:
     Parallelism:   1
     Delay:         10s
    ContainerSpec:
     Image:         redis:3.0.7
    Resources:
    

    The output of service inspect shows if your update paused due to failure:

    $ docker service inspect --pretty redis
    
    ID:             0u6a4s31ybk7yw2wyvtikmu50
    Name:           redis
    ...snip...
    Update status:
     State:      paused
     Started:    11 seconds ago
     Message:    update paused due to failure or early termination of task 9p7ith557h8ndf0ui9s0q951b
    ...snip...
    

    To restart a paused update run docker service update <SERVICE-ID>. For example:

    docker service update redis
    

    To avoid repeating certain update failures, you may need to reconfigure the service by passing flags to docker service update.

  6. Run docker service ps <SERVICE-ID> to watch the rolling update:

    $ docker service ps redis
    
    ID                         NAME     SERVICE  IMAGE        LAST STATE              DESIRED STATE  NODE
    dos1zffgeofhagnve8w864fco  redis.1  redis    redis:3.0.7  Running 37 seconds      Running        worker1
    9l3i4j85517skba5o7tn5m8g0  redis.2  redis    redis:3.0.7  Running About a minute  Running        worker2
    egiuiqpzrdbxks3wxgn8qib1g  redis.3  redis    redis:3.0.7  Running 48 seconds      Running        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.

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