moby/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 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 to update one node every 10 seconds:

   $ docker service create --replicas 3 --name redis --update-delay 10s --update-parallelism 1 redis:3.0.6
   
   0u6a4s31ybk7yw2wyvtikmu50
   

   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:     0u6a4s31ybk7yw2wyvtikmu50
   Name:       redis
   Mode:       REPLICATED
    Replicas:      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. The swarm manager 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:     0u6a4s31ybk7yw2wyvtikmu50
   Name:       redis
   Mode:       REPLICATED
    Replicas:      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        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. You can see that each instances entered the RUNNING state in approximately 10 second increments.

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