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## Description documentation for docker/compose#12166 ## Related issues or tickets [<!-- Related issues, pull requests, or Jira tickets -->](https://docker.atlassian.net/browse/COMP-760) ## Reviews - [ ] Technical review - [ ] Editorial review - [ ] Product review Signed-off-by: Nicolas De Loof <[email protected]>
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--- | ||
title: Using lifecycle hooks with Compose | ||
linkTitle: Use lifecycle hooks | ||
weight: 20 | ||
desription: How to use lifecycle hooks with Docker Compose | ||
keywords: cli, compose, lifecycle, hooks reference | ||
--- | ||
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## Services lifecycle hooks | ||
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When Docker Compose runs a container, it uses two elements, | ||
[ENTRYPOINT and COMMAND](https://github.com/manuals//engine/containers/run.md#default-command-and-options), | ||
to manage what happens when the container starts and stops. | ||
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However, it can sometimes be easier to handle these tasks separately with lifecycle hooks - | ||
commands that run right after the container starts or just before it stops. | ||
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Lifecycle hooks are particularly useful because they can have special privileges | ||
(like running as the root user), even when the container itself runs with lower privileges | ||
for security. This means that certain tasks requiring higher permissions can be done without | ||
compromising the overall security of the container. | ||
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### Post-start hooks | ||
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Post-start hooks are commands that run after the container has started, but there's no | ||
set time for when exactly they will execute. The hook execution timing is not assured during | ||
the execution of the container's `entrypoint`. | ||
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In the example provided: | ||
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- The hook is used to change the ownership of a volume to a non-root user (because volumes | ||
are created with root ownership by default). | ||
- After the container starts, the `chown` command changes the ownership of the `/data` directory to user `1001`. | ||
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```yaml | ||
services: | ||
app: | ||
image: backend | ||
user: 1001 | ||
volumes: | ||
- data:/data | ||
post_start: | ||
- command: chown -R /data 1001:1001 | ||
user: root | ||
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volumes: | ||
data: {} # a Docker volume is created with root ownership | ||
``` | ||
### Pre-stop hooks | ||
Pre-stop hooks are commands that run before the container is stopped by a specific | ||
command (like `docker compose down` or stopping it manually with `Ctrl+C`). | ||
These hooks won't run if the container stops by itself or gets killed suddenly. | ||
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In the following example, before the container stops, the `./data_flush.sh` script is | ||
run to perform any necessary cleanup. | ||
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```yaml | ||
services: | ||
app: | ||
image: backend | ||
pre_stop: | ||
- command: ./data_flush.sh | ||
``` |