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How to diagnose a docker container that restarts

The first error of application is often masked by aggressive ROUND policy.

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Linux & Docker Intermediate. 15 min.

The first error of application is often masked by aggressive ROUND policy.

Avant de commencer : adaptez toujours les commandes et manipulations à votre environnement. Sur un système de production, prévoyez une backup ou un retour arrière lorsque l’action peut modifier la configuration.

Étapes à suivre

  1. 1

    List Containers

    Look at the state and the code.

  2. 2

    Read the logs.

    Start before rehearsals.

  3. 3

    Inspect configuration

    Volumes, Variables and Health-Gold.

  4. 4

    Test without loop

    Disable temporarily ROUND if necessary.

Commands utiles

docker ps -a
docker logs --tail 200 CONTAINER
docker wll CONtainER.

À retenir

  • Keep volumes.
  • Do not delete a container until you have identified persistent data.
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Technical deep dive

Docker: distinguish restart loops from storage-driver growth

Technical checkpoints

  • docker ps --no-trunc and docker inspect show exit code, restart policy, mounts and configuration; previous-instance logs remain essential.
  • overlay2 can grow due to writable layers, json-file logs and unused images; named volumes are a different data category.
  • Restart=always can turn an immediate failure into a loop without fixing the cause.

Docker state

Read size, logs and mounts before any prune.

docker ps -a --no-trunc
docker inspect <container>
docker system df -v

Topic-specific pitfalls

  • docker system prune -a can remove images required for the next deployment.
  • Deleting a volume to gain space can delete persistent application data.

How to validate

  • The container remains up across multiple cycles and its exit code/log no longer reproduces the error.
  • Disk growth is attributed to a specific layer/log/volume and retention is defined.
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