---
description: Apply rolling updates to a service on the swarm
keywords: tutorial, cluster management, swarm, service, rolling-update
title: Apply rolling updates to a service
weight: 70
notoc: true
---

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 7.4.0 container tag. Then you upgrade the service to use the
Redis 7.4.1 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 your Redis tag to the swarm and configure the swarm with a 10 second
    update delay. Note that the following example shows an older Redis tag:

    ```console
    $ docker service create \
      --replicas 3 \
      --name redis \
      --update-delay 10s \
      redis:7.4.0

    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:

    ```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.