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Docker’s official lifecycle-hooks guide documents post_start and pre_stop—not the pre_start hook described in the article behind this headline. The distinction matters: a post-start hook runs after the container starts, and Docker says its timing is not guaranteed relative to the application entrypoint. It therefore does not establish that migrations finish before the app starts.
The author reports using pre_start to replace separate migration and seed services, but the official guide reviewed here does not confirm that hook’s syntax, version support, or behavior. Check the official reference for the exact Compose version you run before removing a working setup.
What Docker’s lifecycle documentation actually confirms
Docker’s Using lifecycle hooks with Compose guide describes hooks for separating certain tasks from a container’s regular entrypoint and command. It documents two lifecycle hooks:
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The guide lists Docker Compose 2.30.0 as the minimum requirement for the hooks it documents. It does not document pre_start. In particular, the existence of post_start does not mean a migration or seed task is guaranteed to finish before the app begins running.
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What the reported pre-start pattern is supposed to do
The article behind this claim describes attaching ordered pre_start steps to an application service instead of maintaining separate migration and seed services. Its author says these steps run in temporary containers before the app service starts, after dependencies have been brought up.
The author also says a step can use a separate image while inheriting the service’s network, environment, and mounts; that steps rerun after service-container recreation, a step-definition change, or an earlier failure; and that failed hook containers remain available for inspection. The author reports that successful output is not retained in Compose output or normal Compose logs.
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Those are the author’s reported behaviors, not guarantees established by the official lifecycle guide. The guide reviewed here does not document pre_start, so it cannot verify those details or establish compatibility for a given Compose release.
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Should you delete separate migration or seed services?
Not based on this claim alone. Before changing a deployment, verify that the exact Compose version in use supports the syntax and ordering your setup needs. Use Docker’s official lifecycle reference for that version; the documented post_start hook is not a substitute when the requirement is “complete setup before the app starts,” because its order relative to the entrypoint is unspecified.
Rank #3
For any proposed replacement, confirm the practical behavior that matters to your system:
- Whether setup is guaranteed to finish before the application process starts.
- When the setup runs again, including after service recreation or a failed attempt.
- How output and failed task containers can be inspected.
- What happens when multiple app replicas or deployments are started.
- How a setup failure affects the application service and dependent services.
- Whether the installed Compose version accepts the feature and configuration.
Do not infer these answers from the name “init container.” The article uses that comparison to describe its reported workflow, but the official page cited above does not establish the behavior of a Compose pre_start hook.
How much weight to give the timing figures
The author reports three-run local timings of 3.9 seconds with no steps, 5.2 seconds with two pre_start steps, and 6.7 seconds with the older pattern. These are measurements from one unspecified laptop setup, not an independently published benchmark. They are not a reliable basis for predicting startup time on another machine or deployment.
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Bottom line
Docker’s lifecycle guide supports post_start and pre_stop, but the reviewed documentation does not confirm the reported pre_start feature or its behavior. Keep established migration and seed services until the official reference for your installed Compose version verifies the pre-start behavior and failure handling your application requires.
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