Apply rolling updates to a service

In a previous step of the tutorial, you scaledthe number of instances of a service. In this part of the tutorial, you deploy a service based on the Redis 3.0.6 container tag. 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 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:

   ]\s+/gm, '')); copying = true; setTimeout(() => copying = false, 2000); ">

   $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-delayflag configures the time delay between updates to a service task or sets of tasks. You can describe the timeTas a combination of the number of secondsTs,minutesTm,or hoursTh.So 10m30sindicates a 10 minute 30 second delay.

   By default the scheduler updates 1 task at a time. You can pass the --update-parallelismflag 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 returnsFAILED,the scheduler pauses the update. You can control the behavior using the --update-failure-actionflag fordocker service createor docker service update.

3. Inspect theredisservice:

   ]\s+/gm, '')); copying = true; setTimeout(() => copying = false, 2000); ">

   $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:3.0.6
   Resources:
   Endpoint Mode: vip
   

4. Now you can update the container image forredis.The swarm manager applies the update to nodes according to theUpdateConfigpolicy:

   ]\s+/gm, '')); copying = true; setTimeout(() => copying = false, 2000); ">

   $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 returnsRUNNING,wait for the specified delay period then start the next task.
   • If, at any time during the update, a task returnsFAILED,pause the update.

5. Rundocker service inspect --pretty redisto see the new image in the desired state:

   ]\s+/gm, '')); copying = true; setTimeout(() => copying = false, 2000); ">

   $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:3.0.7
   Resources:
   Endpoint Mode: vip
   

   The output ofservice inspectshows if your update paused due to failure:

   ]\s+/gm, '')); copying = true; setTimeout(() => copying = false, 2000); ">

   $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 rundocker service update <SERVICE-ID>.For example:

   ]\s+/gm, '')); copying = true; setTimeout(() => copying = false, 2000); ">

   $docker service update redis
   

   To avoid repeating certain update failures, you may need to reconfigure the service by passing flags todocker service update.

6. Rundocker service ps <SERVICE-ID>to watch the rolling update:

   ]\s+/gm, '')); copying = true; setTimeout(() => copying = false, 2000); ">

   $docker service ps redis
   
   NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR
   redis.1.dos1zffgeofhagnve8w864fco redis:3.0.7 worker1 Running Running 37 seconds
   \_ redis.1.88rdo6pa52ki8oqx6dogf04fh redis:3.0.6 worker2 Shutdown Shutdown 56 seconds ago
   redis.2.9l3i4j85517skba5o7tn5m8g0 redis:3.0.7 worker2 Running Running About a minute
   \_ redis.2.66k185wilg8ele7ntu8f6nj6i redis:3.0.6 worker1 Shutdown Shutdown 2 minutes ago
   redis.3.egiuiqpzrdbxks3wxgn8qib1g redis:3.0.7 worker1 Running Running 48 seconds
   \_ redis.3.ctzktfddb2tepkr45qcmqln04 redis:3.0.6 mmanager1 Shutdown Shutdown 2 minutes ago
   

   Before Swarm updates all of the tasks, you can see that some are running redis:3.0.6while others are runningredis:3.0.7.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.