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Rather than conflict with the unexposed task model, change the names of the object-oriented task display to `docker <object> ps`. The command works identically to `docker service tasks`. This change is superficial. This provides a more sensical docker experience while not trampling on the task model that may be introduced as a top-level command at a later date. The following is an example of the display using `docker service ps` with a service named `condescending_cori`: ``` $ docker service ps condescending_cori ID NAME SERVICE IMAGE LAST STATE DESIRED STATE NODE e2cd9vqb62qjk38lw65uoffd2 condescending_cori.1 condescending_cori alpine Running 13 minutes ago Running 6c6d232a5d0e ``` The following shows the output for the node on which the command is running: ```console $ docker node ps self ID NAME SERVICE IMAGE LAST STATE DESIRED STATE NODE b1tpbi43k1ibevg2e94bmqo0s mad_kalam.1 mad_kalam apline Accepted 2 seconds ago Accepted 6c6d232a5d0e e2cd9vqb62qjk38lw65uoffd2 condescending_cori.1 condescending_cori alpine Running 12 minutes ago Running 6c6d232a5d0e 4x609m5o0qyn0kgpzvf0ad8x5 furious_davinci.1 furious_davinci redis Running 32 minutes ago Running 6c6d232a5d0e ``` Signed-off-by: Stephen J Day <stephen.day@docker.com>
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Drain a node on the swarm
In earlier steps of the tutorial, all the nodes have been running with ACTIVE
availability. The swarm manager can assign tasks to any ACTIVE node, so up to
now all nodes have been available to receive tasks.
Sometimes, such as planned maintenance times, you need to set a node to DRAIN
availability. DRAIN availability prevents a node from receiving new tasks
from the swarm manager. It also means the manager stops tasks running on the
node and launches replica tasks on a node with ACTIVE availability.
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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. -
Verify that all your nodes are actively available.
$ docker node ls ID HOSTNAME STATUS AVAILABILITY MANAGER STATUS 1bcef6utixb0l0ca7gxuivsj0 worker2 Ready Active 38ciaotwjuritcdtn9npbnkuz worker1 Ready Active e216jshn25ckzbvmwlnh5jr3g * manager1 Ready Active Leader -
If you aren't still running the
redisservice from the rolling update tutorial, start it now:$ docker service create --replicas 3 --name redis --update-delay 10s redis:3.0.6 c5uo6kdmzpon37mgj9mwglcfw -
Run
docker service ps redisto see how the Swarm manager assigned the tasks to different nodes:$ docker service ps redis ID NAME SERVICE IMAGE LAST STATE DESIRED STATE NODE 7q92v0nr1hcgts2amcjyqg3pq redis.1 redis redis:3.0.6 Running 26 seconds Running manager1 7h2l8h3q3wqy5f66hlv9ddmi6 redis.2 redis redis:3.0.6 Running 26 seconds Running worker1 9bg7cezvedmkgg6c8yzvbhwsd redis.3 redis redis:3.0.6 Running 26 seconds Running worker2In this case the swarm manager distributed one task to each node. You may see the tasks distributed differently among the nodes in your environment.
-
Run
docker node update --availability drain <NODE-ID>to drain a node that had a task assigned to it:docker node update --availability drain worker1 worker1 -
Inspect the node to check its availability:
$ docker node inspect --pretty worker1 ID: 38ciaotwjuritcdtn9npbnkuz Hostname: worker1 Status: State: Ready Availability: Drain ...snip...The drained node shows
DrainforAVAILABILITY. -
Run
docker service ps redisto see how the Swarm manager updated the task assignments for theredisservice:$ docker service ps redis ID NAME SERVICE IMAGE LAST STATE DESIRED STATE NODE 7q92v0nr1hcgts2amcjyqg3pq redis.1 redis redis:3.0.6 Running 4 minutes Running manager1 b4hovzed7id8irg1to42egue8 redis.2 redis redis:3.0.6 Running About a minute Running worker2 9bg7cezvedmkgg6c8yzvbhwsd redis.3 redis redis:3.0.6 Running 4 minutes Running worker2The Swarm manager maintains the desired state by ending the task on a node with
Drainavailability and creating a new task on a node withActiveavailability. -
Run
docker node update --availability active <NODE-ID>to return the drained node to an active state:$ docker node update --availability active worker1 worker1 -
Inspect the node to see the updated state:
$ docker node inspect --pretty worker1 ID: 38ciaotwjuritcdtn9npbnkuz Hostname: worker1 Status: State: Ready Availability: Active
...snip...
When you set the node back to `Active` availability, it can receive new tasks:
* during a service update to scale up
* during a rolling update
* when you set another node to `Drain` availability
* when a task fails on another active node