Custom config in Docker in Nginx - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Docker command?

You run this command to start an nginx container with a custom config file mounted. What will be the output of docker ps immediately after?

Nginx

docker run -d --name mynginx -v /home/user/nginx.conf:/etc/nginx/nginx.conf:ro -p 8080:80 nginx

A No container is created

B Error: Cannot mount /home/user/nginx.conf because it does not exist

C Container exits immediately due to config error

D A running container named 'mynginx' listening on port 8080

💡 Hint

Check if the config file path is correct and the container runs detached.

The command runs nginx detached with a custom config file mounted read-only. If the file exists and is valid, the container runs and listens on port 8080.

❓ Configuration

intermediate

Which Dockerfile snippet correctly copies a custom nginx config?

You want to build a Docker image that uses your custom nginx.conf file inside the container at /etc/nginx/nginx.conf. Which snippet is correct?

A ADD /etc/nginx/nginx.conf nginx.conf

B COPY nginx.conf /etc/nginx/nginx.conf

C COPY /etc/nginx/nginx.conf nginx.conf

D ADD nginx.conf /usr/local/nginx/nginx.conf

💡 Hint

COPY copies from build context to container path.

COPY copies the local file nginx.conf to the container path /etc/nginx/nginx.conf. ADD syntax is similar but less preferred here.

❓ Troubleshoot

advanced

Why does nginx fail to start with this Docker volume mount?

You run:
docker run -d -v /home/user/nginx.conf:/etc/nginx/nginx.conf nginx
But the container exits immediately. What is the most likely cause?

A The host file /home/user/nginx.conf has wrong permissions or is empty

B The container image does not have nginx installed

C The port 80 is already in use on the host

D Docker daemon is not running

💡 Hint

Check the config file content and permissions on the host.

If the config file is empty or unreadable, nginx fails to start and container exits immediately.

🔀 Workflow

advanced

What is the correct workflow to update nginx config in a running container?

You have a running nginx container with a custom config mounted from the host. You want to update the config and apply changes without restarting the container. What should you do?

A Edit the config file on the host and send nginx reload signal inside the container

B Stop the container, replace the config file inside container, then start it

C Rebuild the image with new config and redeploy container

D Edit the config file inside the container directly using docker exec

💡 Hint

Think about how volume mounts reflect changes and how nginx reload works.

Editing the host file updates the mounted config immediately. Sending nginx reload signal applies changes without downtime.

✅ Best Practice

expert

Which approach is best for managing multiple custom nginx configs in Docker for different environments?

You have dev, staging, and production environments each needing different nginx configs. Which is the best Docker setup?

A Build separate Docker images each with its own config baked in

B Use environment variables inside nginx.conf to switch configs dynamically

C Use one image and mount different config files at runtime per environment

D Copy all configs inside one image and switch config by editing container files

💡 Hint

Consider flexibility and image rebuild overhead.

Mounting different config files at runtime allows one image to be reused across environments without rebuilding.