CodeParkCheck the container's state and logs first, then look inside it.
1. Check the state. Run docker ps -a. It shows if the container exited, and its exit code.
2. Read the logs. Run docker logs <container> to read what the app printed. Add -f to follow new output. Many problems show up right here:
- a missing environment variable
- a failed database connection
- a "module not found" error
3. Look inside. If the container is running, open a shell in it with docker exec -it <container> sh. Then check:
- that files are where you expect
- the config, with
env - that the app listens on
0.0.0.0, not only onlocalhost
If the container exits right away, you can't exec into it. Instead, start a shell from the image with docker run --rm -it --entrypoint sh <image>.
4. Inspect the config. docker inspect shows the full config: environment, mounts, networks, command and state.
Common causes:
- Files were excluded by
.dockerignore. localhostpoints at the container itself, not at your machine.- Native dependencies are missing in the image.
- Use docker ps -a to see the state and exit code.
- Use docker logs to read the app's output.
- Use docker exec to open a shell in a running container.
- Use docker run --entrypoint sh for a container that exits at once.
- Use docker inspect to see config, mounts and networks.
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