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45 lines
1.6 KiB
Markdown
45 lines
1.6 KiB
Markdown
5 years ago
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## Executing commands before and after updating
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> **DO NOTE**: Both commands are shell commands executed with `sh`, and therefore require the
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> container to provide the `sh` executable.
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It is possible to execute a *pre-update* command and a *post-update* command
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**inside** every container updated by watchtower. The *pre-update* command is
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executed before stopping the container, and the *post-update* command is
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executed after restarting the container.
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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, with
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`com.centurylinklabs.watchtower.pre-update-command` for the *pre-update*
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command and `com.centurylinklabs.watchtower.lifecycle.post-update` for the
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*post-update* command.
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These labels can be declared as instructions in a Dockerfile:
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```docker
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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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```
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Or be specified as part of the `docker run` command line:
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```bash
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docker run -d \
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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
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```
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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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