Container health checks in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of the health check status command?

You have a Docker container running with a health check configured. You run the command docker inspect --format='{{.State.Health.Status}}' mycontainer. What output do you expect if the container is healthy?

A starting

B unhealthy

C healthy

D exited

💡 Hint

Think about the possible health states Docker reports.

The .State.Health.Status field shows the current health status of the container. If the container passes all health checks, it reports healthy.

🧠 Conceptual

intermediate

Which Dockerfile instruction defines a health check?

In a Dockerfile, which instruction is used to define a container health check?

A STATUSCHECK

B HEALTHCHECK

C RUNHEALTH

D CHECKHEALTH

💡 Hint

It is a single word instruction starting with HEALTH.

The HEALTHCHECK instruction in a Dockerfile defines how Docker tests the container's health.

❓ Configuration

advanced

Identify the correct health check configuration in Dockerfile

Which of the following Dockerfile snippets correctly configures a health check that runs curl -f http://localhost/ || exit 1 every 30 seconds with a timeout of 10 seconds?

A HEALTHCHECK CMD curl -f http://localhost/ || exit 1 --interval=30s --timeout=10s

B HEALTHCHECK --timeout=10s --interval=30s RUN curl -f http://localhost/ || exit 1

C HEALTHCHECK CMD --interval=30s --timeout=10s curl -f http://localhost/ || exit 1

D HEALTHCHECK --interval=30s --timeout=10s CMD curl -f http://localhost/ || exit 1

💡 Hint

Options flags come immediately after HEALTHCHECK, before CMD.

The correct syntax places options like --interval and --timeout right after HEALTHCHECK and before CMD. The command follows CMD.

❓ Troubleshoot

advanced

Why does the health check always show 'starting' status?

You configured a health check in your Docker container, but docker inspect always shows the status as starting. What is the most likely cause?

A The health check command never exits or takes longer than the timeout

B The container is stopped and not running

C The Docker daemon is not running

D The health check command is missing from the Dockerfile

💡 Hint

Think about what 'starting' means in health check lifecycle.

If the health check command never finishes or exceeds the timeout, Docker keeps the status at starting because it never gets a success or failure result.

✅ Best Practice

expert

What is the best practice for health check command exit codes?

For Docker container health checks, which exit code convention should the health check command follow to indicate a healthy or unhealthy state?

A Exit code 0 means healthy; any non-zero exit code means unhealthy

B Exit code 1 means healthy; exit code 0 means unhealthy

C Exit code 2 means healthy; exit code 1 means unhealthy

D Exit code 0 means unhealthy; exit code 1 means healthy

💡 Hint

Think about standard Unix command exit codes.

By Unix convention, exit code 0 means success (healthy), and any non-zero exit code means failure (unhealthy). Docker health checks follow this.