<!--[metadata]>
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title = "Apply rolling updates"
description = "Apply rolling updates to a service on the swarm"
keywords = ["tutorial, cluster management, swarm, service, rolling-update"]
[menu.main]
identifier="swarm-tutorial-rolling-update"
parent="swarm-tutorial"
weight=20
+++
<![end-metadata]-->

# Apply rolling updates to a service

In a previous step of the tutorial, you [scaled](scale-service.md) 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
    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:

    ```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
    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:

    ```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

    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](drain-node.md) in the swarm.