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chore: improve documentation on post/pre-update commands

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Alexandre Menif 2018-10-25 20:52:36 +02:00
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README.md
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@ -277,12 +277,18 @@ docker run -d \
```
## Executing commands before and after updating
For every container that could be updated by watchtower, it is possible to
specify a command that will be executed before stopping the container (a
`pre-update` command), and a command that will be executed after restarting the
container (a `post-update` command). These commands are specified using the
*com.centurylinklabs.watchtower.pre-update-command* and the
*com.centurylinklabs.watchtower.post-update-command* labels.
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.
Both commands are shell commands executed with `sh`, and therefore require the
container to provide the `sh` executable.
The commands are specified using docker container labels, with
*com.centurylinklabs.watchtower.pre-update-command* for the *pre-update*
command and *com.centurylinklabs.watchtower.post-update-command* for the
*post-update* command.
These labels can be declared as instructions in a Dockerfile:
@ -300,3 +306,6 @@ docker run -d \
someimage
```
The failure of a command to execute, identified by an exit code different than
0, should not prevent watchtower from updating the container. Only an error
log statement containing the exit code will be reported.