Apply rolling updates to a service (original) (raw)

In a previous step of the tutorial, youscaled 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.

• 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 namedmanager1.
• 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. So10m30s 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 ofRUNNING, 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 ordocker service update.

• 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  

• 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.
• 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.

• 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 runningredis:7.4.0 while others are running redis:7.4.1. The output above shows the state once the rolling updates are done.

Next, you'll learn how to drain a node in the swarm.