Official Nginx Docker image - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Nginx container startup log

You run the command docker run --name webserver -d nginx. What is the expected output of docker logs webserver?

A nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)

B

2024/01/01 00:00:00 [notice] 1#1: using the "epoll" event method
2024/01/01 00:00:00 [notice] 1#1: nginx/1.25.0
2024/01/01 00:00:00 [notice] 1#1: start worker processes
2024/01/01 00:00:00 [notice] 1#1: start worker process 7

C

Error: Cannot find image 'nginx:latest' locally
Pulling from library/nginx
Digest: sha256:abcdef1234567890
Status: Downloaded newer image for nginx:latest

D docker: command not found

💡 Hint

Check the typical startup log messages for the official Nginx container.

When the Nginx container starts successfully, it logs notices about the event method, version, and worker processes starting. Option B shows this typical log output. Option B shows image pull messages, not logs. Option B is an error if port 80 is busy. Option B is a shell error.

❓ Configuration

intermediate

Mounting custom Nginx config in Docker

You want to run the official Nginx Docker container with your own nginx.conf file located at /home/user/nginx.conf. Which docker run command correctly mounts this config to override the default?

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

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

C docker run -d -p 80:80 -v /home/user/nginx.conf:/usr/local/nginx/conf/nginx.conf:ro nginx

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

💡 Hint

The official Nginx image expects the main config at /etc/nginx/nginx.conf.

The official Nginx Docker image uses /etc/nginx/nginx.conf as the main config file. Mounting your custom config there overrides the default. Option D correctly mounts the file read-only. Option D reverses source and target. Option D uses a wrong path. Option D mounts to conf.d directory which expects snippets, not the main config.

❓ Troubleshoot

advanced

Nginx container fails to start with port binding error

You run docker run -d -p 80:80 nginx but the container exits immediately. Checking logs shows:
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
What is the most likely cause?

A The Docker daemon is not running

B The container lacks permission to bind to port 80 inside the container

C Another process on the host is already using port 80

D The Docker image is corrupted and missing Nginx binaries

💡 Hint

Port binding errors usually mean the port is busy on the host machine.

The error means the host port 80 is already occupied by another process, so Docker cannot bind it for the container. Option C would cause different errors. Option C is unlikely as containers run as root by default. Option C would prevent any Docker commands from working.

🔀 Workflow

advanced

Updating Nginx container with zero downtime

You have a running Nginx container named webserver. You want to update it to a newer Nginx image version without downtime. Which workflow is best?

A Pull new image, start new container on different ports, switch traffic via load balancer, then stop old container

B Pull new image, stop current container, start new container with same ports and volumes

C Remove old container, pull new image, start new container with same ports

D Restart Docker daemon, then pull new image and start new container

💡 Hint

Zero downtime means traffic must not be interrupted during update.

Option A describes a blue-green deployment approach: run new container on different ports, switch traffic, then stop old container. This avoids downtime. Options A and C cause downtime by stopping old container first. Option A is unrelated.

✅ Best Practice

expert

Securing Nginx Docker container with least privileges

Which practice best improves security by running the official Nginx Docker container with least privileges?

A Use the <code>--user</code> flag to run Nginx as a non-root user inside the container

B Run the container as root user to avoid permission issues

C Disable all logging to prevent sensitive data exposure

D Run the container with <code>--privileged</code> flag for full access

💡 Hint

Running as non-root inside containers is a common security best practice.

Running Nginx as a non-root user inside the container reduces risk if compromised. Option A is insecure. Option A disables useful logs and does not improve privilege. Option A grants excessive privileges, increasing risk.

Practice

1. What is the primary purpose of the official Nginx Docker image?

easy

A. To quickly run Nginx inside a container for web serving

B. To build custom Linux kernels

C. To manage databases inside containers

D. To create virtual machines

Solution

1. Step 1: Understand the role of Nginx

   Nginx is a web server used to serve websites and handle web traffic.

2. Step 2: Recognize the Docker image purpose

   The official Nginx Docker image allows running Nginx easily inside containers for web serving.

3. Final Answer:

   To quickly run Nginx inside a container for web serving -> Option A

4. Quick Check:

   Official Nginx Docker image = Quick Nginx container [OK]

Hint: Nginx image runs web server in container fast [OK]

Common Mistakes:

• Confusing Nginx with database or VM tools
• Thinking it builds Linux kernels
• Assuming it manages virtual machines

2. Which Docker command correctly runs the official Nginx image exposing port 80 on the host?

easy

A. docker run -p 80 nginx

B. docker run -p 8080:80 nginx

C. docker run -p 80:80 nginx

D. docker run nginx -p 80:80

Solution

1. Step 1: Understand Docker port mapping syntax

   The correct syntax is docker run -p hostPort:containerPort image.

2. Step 2: Match the command to expose port 80 on host

   docker run -p 80:80 nginx uses -p 80:80 which maps host port 80 to container port 80 correctly.

3. Final Answer:

   docker run -p 80:80 nginx -> Option C

4. Quick Check:

   Port mapping syntax = -p hostPort:containerPort [OK]

Hint: Use -p hostPort:containerPort to expose ports [OK]

Common Mistakes:

• Omitting container port in -p option
• Placing -p after image name
• Using wrong port numbers

3. What will be the result of running this command?

docker run --rm -p 8080:80 nginx

Then accessing http://localhost:8080 in a browser?

medium

A. Connection refused error

B. You will see the default Nginx welcome page

C. 404 Not Found error

D. Docker container will fail to start

Solution

1. Step 1: Analyze the Docker run command

   The command runs Nginx container mapping host port 8080 to container port 80, with --rm to remove container after exit.

2. Step 2: Understand Nginx default behavior

   Nginx serves a default welcome page on port 80 if no custom config is provided.

3. Final Answer:

   You will see the default Nginx welcome page -> Option B

4. Quick Check:

   Default Nginx page served on mapped port [OK]

Hint: Default Nginx page shows if no config mounted [OK]

Common Mistakes:

• Expecting 404 without custom config
• Thinking container fails without volumes
• Confusing port 80 with 8080 inside container

4. You tried to run:

docker run -p 80:80 nginx

but got an error: port is already allocated. What is the best fix?

medium

A. Stop the process using port 80 or use a different host port

B. Change the container port to 8080

C. Remove the Nginx image and pull again

D. Run the container without port mapping

Solution

1. Step 1: Understand the error meaning

   "port is already allocated" means host port 80 is in use by another process.

2. Step 2: Choose a fix for port conflict

   Stopping the process using port 80 or mapping to a different host port avoids conflict.

3. Final Answer:

   Stop the process using port 80 or use a different host port -> Option A

4. Quick Check:

   Port conflict fix = stop process or change host port [OK]

Hint: Port conflict means host port busy; change or free it [OK]

Common Mistakes:

• Changing container port instead of host port
• Deleting image won't fix port conflict
• Running without port mapping disables access

5. You want to customize Nginx by using your own nginx.conf file located at /home/user/nginx.conf. Which Docker command correctly mounts this config into the container?

hard

A. docker run -v /etc/nginx/nginx.conf:/home/user/nginx.conf -p 8080:80 nginx

B. docker run -v /home/user/nginx.conf:/usr/local/nginx/nginx.conf -p 8080:80 nginx

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

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

Solution

1. Step 1: Identify correct Nginx config path inside container

   The main config file path in official Nginx image is /etc/nginx/nginx.conf.

2. Step 2: Use volume mount syntax to map host config

   Mount host file /home/user/nginx.conf to container path /etc/nginx/nginx.conf with read-only flag :ro.

3. Final Answer:

   docker run -v /home/user/nginx.conf:/etc/nginx/nginx.conf:ro -p 8080:80 nginx -> Option D

4. Quick Check:

   Mount host config to /etc/nginx/nginx.conf with :ro [OK]

Hint: Mount config to /etc/nginx/nginx.conf with :ro for safety [OK]

Common Mistakes:

• Reversing source and target paths in -v option
• Mounting to wrong container config directory
• Omitting :ro to prevent accidental changes