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Feat/lifecycle hooks (#351)

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* feat(update): add lifecycle hooks to the update action

* fix(ci): add bash tests for lifecycle-hooks to the ci workflow

* fix(ci): move integration tests to an isolated step

* fix(ci): fix malformed all-contributors json

* fix(ci): disable automatic bash test until we figure out a reasonable way to run it in circleci
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Simon Aronsson 2019-07-27 01:37:16 +02:00 • committed by GitHub
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## Executing commands before and after updating
> **DO NOTE**: Both commands are shell commands executed with `sh`, and therefore require the
> container to provide the `sh` executable.
It is possible to execute a *pre-update* command and a *post-update* command
**inside** every container updated by watchtower. The *pre-update* command is
executed before stopping the container, and the *post-update* command is
executed after restarting the container.
This feature is disabled by default. To enable it, you need to set the option
`--enable-lifecycle-hooks` on the command line, or set the environment variable
`WATCHTOWER_LIFECYCLE_HOOKS` to true.
### Specifying update commands
The commands are specified using docker container labels, with
`com.centurylinklabs.watchtower.pre-update-command` for the *pre-update*
command and `com.centurylinklabs.watchtower.lifecycle.post-update` for the
*post-update* command.
These labels can be declared as instructions in a Dockerfile:
```docker
LABEL com.centurylinklabs.watchtower.lifecycle.pre-update="/dump-data.sh"
LABEL com.centurylinklabs.watchtower.lifecycle.post-update="/restore-data.sh"
```
Or be specified as part of the `docker run` command line:
```bash
docker run -d \
--label=com.centurylinklabs.watchtower.lifecycle.pre-update="/dump-data.sh" \
--label=com.centurylinklabs.watchtower.lifecycle.post-update="/restore-data.sh" \
someimage
```
### Execution failure
The failure of a command to execute, identified by an exit code different than
0, will not prevent watchtower from updating the container. Only an error
log statement containing the exit code will be reported.