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Docker Advanced: Builds and Containers That Hold Up in Production
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Docker Advanced: Builds and Containers That Hold Up in Production

Check Yourself: Beyond One Compose File

Five scenario questions on merged ports, override files, profiles, watch and CI logins. If you miss more than one, reread the lessons in this section.

5 min DockerSecurityPerformance OptimizationDeployment and Containers Advanced
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1. compose.yaml publishes 127.0.0.1:8471:80 for the web service. compose.prod.yaml lists ports with 8080:80 for the same service. You run docker compose with both files. Which ports are published?
Only 8080, because the later file wins. Both. Lists such as ports are added together across files, so production also publishes the development port. Only 8471, because the first file wins. Neither, because the two files conflict.
2. Why should a production server start Compose with an explicit file list instead of plain docker compose up?
An explicit file list makes containers start faster. Plain docker compose up does not work on Linux. Compose reads compose.override.yaml automatically if it is in the folder, so development settings can end up in production. docker compose up ignores profiles unless files are listed.
3. A Compose file has a database admin tool with profiles debug. A teammate runs docker compose up and asks why the tool did not start. What do you tell them?
Services with a profile start only when the profile is named, for example docker compose --profile debug up. The service must be listed first in the file. Profiles only work with docker compose watch. The tool crashed, check its logs.
4. During development you use docker compose watch with a sync action for the src folder. You edit a file in src. What happens?
Nothing happens until you run docker compose up again. Compose copies the changed file into the running container, without rebuilding the image. The file is bind mounted, so the container sees it immediately. Compose rebuilds the image and recreates the container.
5. How should a CI job log in to a private registry?
Commit a config.json with the auth value to the repository. Use the personal account of the team lead so it always has access. Take the token from the CI secret store and pass it to docker login with --password-stdin, using a token with the smallest scope that works. docker login with -p and the password in the job script.

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Five scenario questions on merged ports, override files, profiles, watch and CI logins. If you miss more than one, reread the lessons in this section.

Duration
5 min
Last update
08/01/2026
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