Performing and Monitoring Rolling Updates in Docker Swarm

`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: ```console $ 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:7.4.0 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: ```console $ docker service update --image redis:7.4.1 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 start 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: ```console $ 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:7.4.1 Resources: Endpoint Mode: vip ``` The output of `service inspect` shows if your update paused due to failure: ```console $ 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: ```console $ 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: ```console $ docker service ps redis NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR redis.1.dos1zffgeofhagnve8w864fco redis:7.4.1 worker1 Running Running 37 seconds \_ redis.1.88rdo6pa52ki8oqx6dogf04fh redis:7.4.0 worker2 Shutdown Shutdown 56 seconds ago redis.2.9l3i4j85517skba5o7tn5m8g0 redis:7.4.1 worker2 Running Running About a minute \_ redis.2.66k185wilg8ele7ntu8f6nj6i redis:7.4.0 worker1 Shutdown Shutdown 2 minutes ago redis.3.egiuiqpzrdbxks3wxgn8qib1g redis:7.4.1 worker1 Running Running 48 seconds \_ redis.3.ctzktfddb2tepkr45qcmqln04 redis:7.4.0 mmanager1 Shutdown Shutdown 2 minutes ago ``` Before Swarm updates all of the tasks, you can see that some are running `redis:7.4.0` while others are running `redis:7.4.1`. The output above shows the state once the rolling updates are done. ## Next steps Next, you'll learn how to drain a node in the swarm. {{< button text="Drain a node" url="drain-node.md" >}}

This section details how Docker Swarm's rolling updates are applied, including stopping a task, scheduling updates, and managing failures. It provides commands to inspect the service, restart paused updates, and monitor the update process using `docker service ps`. The example demonstrates how to observe tasks running different versions of the image during the update process and how to check for paused updates due to failures. The next step is to learn how to drain a node.