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Command: node drain

The node drain command is used to toggle drain mode on a given node. Drain mode prevents any new tasks from being allocated to the node, and begins migrating all existing allocations away.

The exact behavior of drained allocations depends on the job type:

  • Allocations for service jobs will be migrated according to their migrate block until the drain's deadline is reached. These allocations are not considered rescheduled and their previous reschedule attempts will not be propagated to any replacement allocations.
  • Allocations for batch and sysbatch jobs will wait until they complete or the drain's deadline is reached, whichever comes first. These allocations will not be replaced.
  • Allocations for system job allocations will be drained last by default. These allocations will be stopped but not replaced.

By default the node drain command blocks until a node is done draining and all allocations have terminated. Canceling the node drain command will not cancel the drain. Drains may be canceled by using the -disable parameter below.

When draining more than one node at a time, it is recommended you first disable scheduling eligibility on all nodes that will be drained. For example if you are decommissioning an entire class of nodes, first run node eligibility -disable on all of their node IDs, and then run node drain -enable. This will ensure allocations drained from the first node are not placed on another node about to be drained.

The node status command compliments this nicely by providing the current drain status of a given node.

See the Workload Migration guide for detailed examples of node draining.

Usage

nomad node drain [options] <node>

A -self flag can be used to drain the local node. If this is not supplied, a node ID or prefix must be provided. If there is an exact match, the drain mode will be adjusted for that node. Otherwise, a list of matching nodes and information will be displayed.

It is also required to pass one of -enable or -disable, depending on which operation is desired.

If ACLs are enabled, this option requires a token with the 'node:write' capability.

General Options

  • -address=<addr>: The address of the Nomad server. Overrides the NOMAD_ADDR environment variable if set. Defaults to http://127.0.0.1:4646.

  • -region=<region>: The region of the Nomad server to forward commands to. Overrides the NOMAD_REGION environment variable if set. Defaults to the Agent's local region.

  • -no-color: Disables colored command output. Alternatively, NOMAD_CLI_NO_COLOR may be set. This option takes precedence over -force-color.

  • -force-color: Forces colored command output. This can be used in cases where the usual terminal detection fails. Alternatively, NOMAD_CLI_FORCE_COLOR may be set. This option has no effect if -no-color is also used.

  • -ca-cert=<path>: Path to a PEM encoded CA cert file to use to verify the Nomad server SSL certificate. Overrides the NOMAD_CACERT environment variable if set.

  • -ca-path=<path>: Path to a directory of PEM encoded CA cert files to verify the Nomad server SSL certificate. If both -ca-cert and -ca-path are specified, -ca-cert is used. Overrides the NOMAD_CAPATH environment variable if set.

  • -client-cert=<path>: Path to a PEM encoded client certificate for TLS authentication to the Nomad server. Must also specify -client-key. Overrides the NOMAD_CLIENT_CERT environment variable if set.

  • -client-key=<path>: Path to an unencrypted PEM encoded private key matching the client certificate from -client-cert. Overrides the NOMAD_CLIENT_KEY environment variable if set.

  • -tls-server-name=<value>: The server name to use as the SNI host when connecting via TLS. Overrides the NOMAD_TLS_SERVER_NAME environment variable if set.

  • -tls-skip-verify: Do not verify TLS certificate. This is highly not recommended. Verification will also be skipped if NOMAD_SKIP_VERIFY is set.

  • -token: The SecretID of an ACL token to use to authenticate API requests with. Overrides the NOMAD_TOKEN environment variable if set.

Drain Options

  • -enable: Enable node drain mode.

  • -disable: Disable node drain mode.

  • -deadline: Set the deadline by which all allocations must be moved off the node. Remaining allocations after the deadline are removed from the node, regardless of their migrate block. Defaults to 1 hour.

  • -detach: Return immediately instead of entering monitor mode.

  • -monitor: Enter monitor mode directly without modifying the drain status.

  • -force: Remove allocations off the node immediately, regardless of the allocation's migrate block. This will include system jobs and CSI plugins if -ignore-system is not also set, and is not safe for use with CSI node plugins if the volumes are not being detached externally (for example, a cloud VM is being terminated).

  • -no-deadline: No deadline allows the allocations to drain off the node, ignoring the default 1 hour deadline before allocations are removed regardless of their migrate block.

  • -ignore-system: Ignore system allows the drain to complete without stopping system job allocations. By default system jobs (and CSI plugins) are stopped last.

  • -keep-ineligible: Keep ineligible will maintain the node's scheduling ineligibility even if the drain is being disabled. This is useful when an existing drain is being cancelled but additional scheduling on the node is not desired.

  • -m: Message for the drain update operation. Registered in drain metadata as "message" during drain enable and "cancel_message" during drain disable.

  • -meta <key>=<value>: Custom metadata to store on the drain operation, can be used multiple times.

  • -self: Drain the local node.

  • -yes: Automatic yes to prompts.

Examples

Enable drain mode on node with ID prefix "4d2ba53b":

$ nomad node drain -enable f4e8a9e5 -m "node maintenance"
Are you sure you want to enable drain mode for node "f4e8a9e5-30d8-3536-1e6f-cda5c869c35e"? [y/N] y
2018-03-30T23:13:16Z: Ctrl-C to stop monitoring: will not cancel the node drain
2018-03-30T23:13:16Z: Node "f4e8a9e5-30d8-3536-1e6f-cda5c869c35e" drain strategy set
2018-03-30T23:13:17Z: Alloc "1877230b-64d3-a7dd-9c31-dc5ad3c93e9a" marked for migration
2018-03-30T23:13:17Z: Alloc "1877230b-64d3-a7dd-9c31-dc5ad3c93e9a" draining
2018-03-30T23:13:17Z: Alloc "1877230b-64d3-a7dd-9c31-dc5ad3c93e9a" status running -> complete
2018-03-30T23:13:29Z: Alloc "3fce5308-818c-369e-0bb7-f61f0a1be9ed" marked for migration
2018-03-30T23:13:29Z: Alloc "3fce5308-818c-369e-0bb7-f61f0a1be9ed" draining
2018-03-30T23:13:30Z: Alloc "3fce5308-818c-369e-0bb7-f61f0a1be9ed" status running -> complete
2018-03-30T23:13:41Z: Alloc "9a98c5aa-a719-2f34-ecfc-0e6268b5d537" marked for migration
2018-03-30T23:13:41Z: Alloc "9a98c5aa-a719-2f34-ecfc-0e6268b5d537" draining
2018-03-30T23:13:41Z: Node "f4e8a9e5-30d8-3536-1e6f-cda5c869c35e" has marked all allocations for migration
2018-03-30T23:13:42Z: Alloc "9a98c5aa-a719-2f34-ecfc-0e6268b5d537" status running -> complete
2018-03-30T23:13:42Z: All allocations on node "f4e8a9e5-30d8-3536-1e6f-cda5c869c35e" have stopped.

Enable drain mode on the local node:

$ nomad node drain -enable -self
...

Enable drain mode but do not stop system jobs:

$ nomad node drain -enable -ignore-system 4d2ba53b
...

Disable drain mode but keep the node ineligible for scheduling. Useful for inspecting the current state of a misbehaving node without Nomad trying to start or migrate allocations:

$ nomad node drain -disable -keep-ineligible 4d2ba53b
...

Enable drain mode and detach from monitoring, then reattach later:

$ nomad node drain -enable -detach -self
...
$ nomad node drain -self -monitor
...
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