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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: Running Under Load

Five scenario questions on exit code 137, CPU limits, health status, restart policies and log options. If you miss more than one, reread the lessons in this section.

5 min DockerSecurityPerformance OptimizationDeployment and Containers Advanced
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1. A container keeps exiting with code 137 and docker inspect shows OOMKilled=true. What does that tell you?
The CPU limit was too low. The app crashed with a Python error. Someone ran docker stop. The processes in the container went over its memory limit and the kernel killed them.
2. You set --cpus 0.5 on a busy worker. What happens when the worker wants more CPU?
It is restarted by Docker. It is marked unhealthy. It runs slower, because it only gets half of one core over time. Nothing is killed. It gets more CPU automatically when the host is idle.
3. A container has restart unless-stopped and a health check. The app hangs and the container shows unhealthy for an hour. Docker Compose did not restart it. Why?
unless-stopped never restarts containers. Plain Docker and Compose only mark a container unhealthy. The restart policy reacts to the process exiting, not to the health status. The restart policy needs a few hours before it acts. The health check must be in the Compose file, not the image, to trigger restarts.
4. A one-off database migration job is defined with restart always in Compose. What will happen after it finishes successfully?
It stops, because always only applies to failed containers. Docker asks before restarting. Compose removes the container automatically. It runs again, and again, because always restarts the container whenever it exits.
5. You set log options max-size 10m and max-file 3 in daemon.json and restarted Docker. A container created last week still has logs growing past 30 MB. Why?
The limit only applies to the local driver. Log options are fixed when a container is created. The old container keeps its old settings until it is recreated. daemon.json is ignored on Docker Desktop. max-file 3 means three files per day.

About

Five scenario questions on exit code 137, CPU limits, health status, restart policies and log options. If you miss more than one, reread the lessons in this section.

Duration
5 min
Last update
08/01/2026
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