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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: Production Concerns

Five scenario questions on read-only containers, tmpfs, deployment gaps, health checks and where Docker Desktop belongs. If you miss more than one, reread the lessons in this section.

5 min DockerSecurityPerformance OptimizationDeployment and Containers Advanced
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1. You run nginx with read-only root filesystem and it exits right away. What is the quickest way to find out which paths it needs to write?
Add --privileged so it can write. Turn read-only off, because nginx does not support it. Mount a volume over the whole root folder. Run it once without read-only and use docker diff to list the files it added or changed, then give those paths a tmpfs or fix them in the image.
2. Your app stores user uploads in /uploads. You add read-only and put a tmpfs on /uploads. What will happen?
Uploads are copied into the image on the next build. Uploads are written to the host disk. Uploads work until the container restarts, then they are all gone, because tmpfs lives in memory. Uploads fail because tmpfs is read-only too.
3. On one host, you deploy a new version with docker compose up -d. A client counting requests during the deploy shows some failed requests. Why?
Compose always restarts the proxy too. Compose stops the old container before the new one is created and ready, so for a moment nothing answers. The new image is broken. The client is too fast for Docker.
4. In the blue and green pattern, why does the new copy need a health check before you switch the proxy?
Docker refuses to reload nginx without a health check. Without a health check, the new container gets no IP address. So docker compose up --wait waits until the app is really ready. Without it, wait returns as soon as the container is running, and traffic can reach an app that is still starting. The health check restarts the old copy automatically.
5. A company with 400 employees wants to run its production containers on a Windows server with Docker Desktop. What is the best advice?
Docker Desktop is the recommended way to run production on Windows. It is fine as long as nobody logs out of the server. Use Docker Engine on Linux servers. Docker Desktop is a developer app that runs in a user session, and at that company size it needs a paid subscription. Docker Desktop and Docker Engine have the same licence terms.

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Five scenario questions on read-only containers, tmpfs, deployment gaps, health checks and where Docker Desktop belongs. If you miss more than one, reread the lessons in this section.

Duration
5 min
Last update
08/01/2026
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