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---
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layout: docs
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page_title: lifecycle Stanza - Job Specification
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sidebar_title: lifecycle
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description: |-
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The "lifecycle" stanza configures when a task is run within the lifecycle of a
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task group
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2020-03-25 16:57:53 +00:00
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---
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2020-04-07 18:22:04 +00:00
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# `lifecycle` Stanza
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<Placement groups={['job', 'group', 'task', 'lifecycle']} />
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The `lifecycle` stanza is used to express task dependencies in Nomad and
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configures when a task is run within the lifecycle of a task group.
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Main tasks are tasks that do not have a `lifecycle` stanza. Lifecycle task hooks
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are run in relation to the main tasks. Tasks can be run as Prestart Hooks, which
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ensures the prestart task is run before the main tasks are run.
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Tasks can be run with an additional parameter to indicate that they are
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sidecars, which ensures that they are running over the duration of the whole
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task group. This will allow you to run a long-lived task in a task group for a
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batch job. The absence of the sidecar flag indicates that the task is ephemeral
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and the task will not be restarted if it completes successfully. This allows you
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to run an ephemeral prestart task in a task group for a service job, which can
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serve as initialization that occurs before the main services are started.
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2020-03-31 17:24:27 +00:00
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Learn more about Nomad's task dependencies on the [HashiCorp Learn website][learn-taskdeps].
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```hcl
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job "docs" {
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group "example" {
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task "init" {
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lifecycle {
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hook = "prestart"
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}
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...
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}
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task "logging" {
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lifecycle {
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hook = "prestart"
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sidecar = true
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}
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...
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}
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task "main" {
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...
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}
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}
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}
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```
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## `lifecycle` Parameters
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- `hook` `(string: "prestart")` - Specifies when a task should be run within
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the lifecycle of a group. Currently only Prestart Hooks are supported.
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- `sidecar` `(bool: false)` - Controls whether or not a task is ephemeral or
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long-lived within the task group. If a lifecycle task is ephemeral (`sidecar =
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false`), the task will not be restarted after it completes successfully. If a
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lifecycle task is long-lived (`sidecar = true`) and it terminates, it will be
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restarted as long as the task group is running in its allocation.
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2020-03-31 17:24:27 +00:00
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[learn-taskdeps]: https://learn.hashicorp.com/nomad?track=task-deps&utm_source=WEBSITE&utm_medium=WEB_IO&utm_offer=ARTICLE_PAGE&utm_content=DOCS#task-deps
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