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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>
130 lines
4.2 KiB
Markdown
130 lines
4.2 KiB
Markdown
<!--[metadata]>
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+++
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title = "Drain a node"
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description = "Drain nodes on the Swarm"
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keywords = ["tutorial, cluster management, swarm, service, drain"]
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[menu.main]
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identifier="swarm-tutorial-drain-node"
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parent="swarm-tutorial"
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weight=21
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+++
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<![end-metadata]-->
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# Drain a node on the swarm
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In earlier steps of the tutorial, all the nodes have been running with `ACTIVE`
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availability. The swarm manager can assign tasks to any `ACTIVE` node, so up to
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now all nodes have been available to receive tasks.
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Sometimes, such as planned maintenance times, you need to set a node to `DRAIN`
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availability. `DRAIN` availability prevents a node from receiving new tasks
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from the swarm manager. It also means the manager stops tasks running on the
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node and launches replica tasks on a node with `ACTIVE` availability.
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1. If you haven't already, open a terminal and ssh into the machine where you
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run your manager node. For example, the tutorial uses a machine named
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`manager1`.
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2. Verify that all your nodes are actively available.
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```bash
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$ docker node ls
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ID HOSTNAME STATUS AVAILABILITY MANAGER STATUS
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1bcef6utixb0l0ca7gxuivsj0 worker2 Ready Active
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38ciaotwjuritcdtn9npbnkuz worker1 Ready Active
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e216jshn25ckzbvmwlnh5jr3g * manager1 Ready Active Leader
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```
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3. If you aren't still running the `redis` service from the [rolling
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update](rolling-update.md) tutorial, start it now:
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```bash
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$ docker service create --replicas 3 --name redis --update-delay 10s redis:3.0.6
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c5uo6kdmzpon37mgj9mwglcfw
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```
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4. Run `docker service ps redis` to see how the Swarm manager assigned the
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tasks to different nodes:
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```bash
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$ docker service ps redis
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ID NAME SERVICE IMAGE LAST STATE DESIRED STATE NODE
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7q92v0nr1hcgts2amcjyqg3pq redis.1 redis redis:3.0.6 Running 26 seconds Running manager1
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7h2l8h3q3wqy5f66hlv9ddmi6 redis.2 redis redis:3.0.6 Running 26 seconds Running worker1
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9bg7cezvedmkgg6c8yzvbhwsd redis.3 redis redis:3.0.6 Running 26 seconds Running worker2
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```
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In this case the swarm manager distributed one task to each node. You may
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see the tasks distributed differently among the nodes in your environment.
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5. Run `docker node update --availability drain <NODE-ID>` to drain a node that
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had a task assigned to it:
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```bash
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docker node update --availability drain worker1
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worker1
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```
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6. Inspect the node to check its availability:
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```bash
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$ docker node inspect --pretty worker1
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ID: 38ciaotwjuritcdtn9npbnkuz
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Hostname: worker1
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Status:
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State: Ready
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Availability: Drain
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...snip...
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```
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The drained node shows `Drain` for `AVAILABILITY`.
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7. Run `docker service ps redis` to see how the Swarm manager updated the
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task assignments for the `redis` service:
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```bash
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$ docker service ps redis
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ID NAME SERVICE IMAGE LAST STATE DESIRED STATE NODE
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7q92v0nr1hcgts2amcjyqg3pq redis.1 redis redis:3.0.6 Running 4 minutes Running manager1
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b4hovzed7id8irg1to42egue8 redis.2 redis redis:3.0.6 Running About a minute Running worker2
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9bg7cezvedmkgg6c8yzvbhwsd redis.3 redis redis:3.0.6 Running 4 minutes Running worker2
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```
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The Swarm manager maintains the desired state by ending the task on a node
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with `Drain` availability and creating a new task on a node with `Active`
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availability.
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8. Run `docker node update --availability active <NODE-ID>` to return the
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drained node to an active state:
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```bash
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$ docker node update --availability active worker1
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worker1
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```
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9. Inspect the node to see the updated state:
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```bash
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$ docker node inspect --pretty worker1
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ID: 38ciaotwjuritcdtn9npbnkuz
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Hostname: worker1
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Status:
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State: Ready
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Availability: Active
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...snip...
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```
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When you set the node back to `Active` availability, it can receive new tasks:
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* during a service update to scale up
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* during a rolling update
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* when you set another node to `Drain` availability
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* when a task fails on another active node
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