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68 lines
3.0 KiB
Markdown
68 lines
3.0 KiB
Markdown
## Executing commands before and after updating
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!!! note
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These are shell commands executed with `sh`, and therefore require the container to provide the `sh`
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executable.
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It is possible to execute _pre/post\-check_ and _pre/post\-update_ commands
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**inside** every container updated by watchtower.
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- The _pre-check_ command is executed for each container prior to every update cycle.
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- The _pre-update_ command is executed before stopping the container when an update is about to start.
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- The _post-update_ command is executed after restarting the updated container
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- The _post-check_ command is executed for each container post every update cycle.
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This feature is disabled by default. To enable it, you need to set the option
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`--enable-lifecycle-hooks` on the command line, or set the environment variable
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`WATCHTOWER_LIFECYCLE_HOOKS` to `true`.
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### Specifying update commands
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The commands are specified using docker container labels, the following are currently available:
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| Type | Docker Container Label |
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| ----------- | ------------------------------------------------------ |
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| Pre Check | `com.centurylinklabs.watchtower.lifecycle.pre-check` |
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| Pre Update | `com.centurylinklabs.watchtower.lifecycle.pre-update` |
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| Post Update | `com.centurylinklabs.watchtower.lifecycle.post-update` |
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| Post Check | `com.centurylinklabs.watchtower.lifecycle.post-check` |
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These labels can be declared as instructions in a Dockerfile (with some example .sh files) or be specified as part of
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the `docker run` command line:
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=== "Dockerfile"
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```docker
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LABEL com.centurylinklabs.watchtower.lifecycle.pre-check="/sync.sh"
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LABEL com.centurylinklabs.watchtower.lifecycle.pre-update="/dump-data.sh"
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LABEL com.centurylinklabs.watchtower.lifecycle.post-update="/restore-data.sh"
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LABEL com.centurylinklabs.watchtower.lifecycle.post-check="/send-heartbeat.sh"
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```
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=== "docker run"
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```bash
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docker run -d \
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--label=com.centurylinklabs.watchtower.lifecycle.pre-check="/sync.sh" \
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--label=com.centurylinklabs.watchtower.lifecycle.pre-update="/dump-data.sh" \
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--label=com.centurylinklabs.watchtower.lifecycle.post-update="/restore-data.sh" \
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someimage --label=com.centurylinklabs.watchtower.lifecycle.post-check="/send-heartbeat.sh" \
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```
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### Timeouts
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The timeout for all lifecycle commands is 60 seconds. After that, a timeout will
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occur, forcing Watchtower to continue the update loop.
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#### Pre-update timeouts
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For the `pre-update` lifecycle command, it is possible to override this timeout to
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allow the script to finish before forcefully killing it. This is done by adding the
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label `com.centurylinklabs.watchtower.lifecycle.pre-update-timeout` followed by
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the timeout expressed in minutes.
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If the label value is explicitly set to `0`, the timeout will be disabled.
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### Execution failure
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The failure of a command to execute, identified by an exit code different than
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0, will not prevent watchtower from updating the container. Only an error
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log statement containing the exit code will be reported.
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