Apply rolling updates (Engine)

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:

   ```bash $ 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:

   ```bash $ docker service inspect –pretty redis

   ID: 0u6a4s31ybk7yw2wyvtikmu50 Name: redis Service Mode: Replicated Replicas: 3 Placement: Strategy: Spread UpdateConfig: Parallelism: 1 Delay: 10s ContainerSpec: Image: redis:3.0.6 Resources: Endpoint Mode: vip ```

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

   bash $ 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:

   ```bash $ docker service inspect –pretty redis

   ID: 0u6a4s31ybk7yw2wyvtikmu50 Name: redis Service Mode: Replicated Replicas: 3 Placement: Strategy: Spread UpdateConfig: Parallelism: 1 Delay: 10s ContainerSpec: Image: redis:3.0.7 Resources: Endpoint Mode: vip ```

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

   ```bash $ 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:

   bash 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:

   ```bash $ docker service ps redis

   NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR redis.1.dos1zffgeofhagnve8w864fco redis:3.0.7 worker1 Running Running 37 seconds _ redis.1.88rdo6pa52ki8oqx6dogf04fh redis:3.0.6 worker2 Shutdown Shutdown 56 seconds ago redis.2.9l3i4j85517skba5o7tn5m8g0 redis:3.0.7 worker2 Running Running About a minute _ redis.2.66k185wilg8ele7ntu8f6nj6i redis:3.0.6 worker1 Shutdown Shutdown 2 minutes ago redis.3.egiuiqpzrdbxks3wxgn8qib1g redis:3.0.7 worker1 Running Running 48 seconds _ redis.3.ctzktfddb2tepkr45qcmqln04 redis:3.0.6 mmanager1 Shutdown Shutdown 2 minutes ago ```

   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.