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 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:

    $ 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:

    $ 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:

    $ 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:

    $ 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:

    $ 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:

    $ 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:

    $ 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.

Drain a node