Docker inspect for detailed info - Mini Project: Build & Apply

Docker inspect for detailed info

📖 Scenario: You are managing Docker containers on your local machine. You want to learn how to get detailed information about a running container to understand its settings and status.

🎯 Goal: Learn how to use the docker inspect command to get detailed JSON information about a Docker container.

📋 What You'll Learn

Create a Docker container named exactly my_nginx running the nginx image

Use docker inspect to get detailed info about the my_nginx container

Extract and display the container's IP address from the inspect output

💡 Why This Matters

🌍 Real World

Docker inspect is used daily by developers and system admins to check container settings, network info, and troubleshoot issues.

💼 Career

Knowing how to inspect containers helps in debugging, monitoring, and managing containerized applications in DevOps roles.

1

Create a Docker container named my_nginx

Run the command to create and start a Docker container named my_nginx using the nginx image in detached mode.

Docker

# Run the docker command to create and start the container
# Your code here

Hint

Use docker run -d --name my_nginx nginx to start the container in the background.

2

Use docker inspect to get detailed info about my_nginx

Run the command docker inspect my_nginx to get detailed JSON information about the container named my_nginx.

Docker

docker run -d --name my_nginx nginx
# Run docker inspect on my_nginx
# Your code here

Hint

Use docker inspect my_nginx to see detailed info about the container.

3

Extract the container's IP address from the inspect output

Use docker inspect with the --format option and Go template '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' to extract and display the IP address of the my_nginx container.

Docker

docker run -d --name my_nginx nginx
docker inspect my_nginx
# Extract and display the IP address of my_nginx
# Your code here

Hint

Use docker inspect --format='{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' my_nginx to get the IP address.

4

Display the IP address of the my_nginx container

Run the command to display only the IP address of the my_nginx container using docker inspect with the correct format option.

Docker

docker run -d --name my_nginx nginx
docker inspect my_nginx
docker inspect --format='{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' my_nginx
# Display the IP address
# Your code here

Hint

The IP address usually starts with 172. or 192. depending on your Docker network.

Practice

1. What is the primary purpose of the docker inspect command?

easy

A. To start a new Docker container

B. To show detailed information about Docker objects like containers and images

C. To remove unused Docker images

D. To list all running Docker containers

Solution

1. Step 1: Understand the command's function

   docker inspect is used to get detailed JSON data about Docker objects such as containers, images, volumes, and networks.

2. Step 2: Compare with other Docker commands

   Starting containers is done with docker run, removing images with docker rmi, and listing containers with docker ps. None of these show detailed info like docker inspect.

3. Final Answer:

   To show detailed information about Docker objects like containers and images -> Option B

4. Quick Check:

   docker inspect = detailed info [OK]

Hint: Remember: inspect means look closely at details [OK]

Common Mistakes:

• Confusing inspect with commands that start or list containers
• Thinking inspect modifies containers
• Assuming inspect only works for images

2. Which of the following is the correct syntax to inspect a container named myapp?

easy

A. docker inspect myapp

B. docker inspect -n myapp

C. docker inspect --container myapp

D. docker inspect container=myapp

Solution

1. Step 1: Recall the basic syntax of docker inspect

   The command is docker inspect [OPTIONS] NAME|ID. No extra flags are needed to specify container name.

2. Step 2: Evaluate each option

   docker inspect myapp matches the correct syntax. Options B, C, and D use invalid flags or formats not recognized by Docker.

3. Final Answer:

   docker inspect myapp -> Option A

4. Quick Check:

   docker inspect + container name = correct syntax [OK]

Hint: Use just 'docker inspect' plus container name or ID [OK]

Common Mistakes:

• Adding unnecessary flags like -n or --container
• Using equal signs in command arguments
• Confusing inspect syntax with other Docker commands

3. What will be the output of the command docker inspect --format='{{.NetworkSettings.IPAddress}}' mycontainer?

medium

A. An error because the format is incorrect

B. The container's environment variables

C. The container's mounted volumes

D. The IP address assigned to the container named mycontainer

Solution

1. Step 1: Understand the --format option

   The --format flag allows extracting specific fields from the JSON output using Go templates. Here, {{.NetworkSettings.IPAddress}} targets the container's IP address.

2. Step 2: Match the template to the expected output

   This template returns the IP address string of the container named mycontainer. Other options like environment variables or volumes require different template paths.

3. Final Answer:

   The IP address assigned to the container named mycontainer -> Option D

4. Quick Check:

   --format with IPAddress = container IP [OK]

Hint: Use --format with .NetworkSettings.IPAddress for container IP [OK]

Common Mistakes:

• Confusing IPAddress with environment variables
• Using wrong template syntax causing errors
• Expecting full JSON output instead of filtered data

4. You run docker inspect --format='{{.Config.Env}}' mycontainer but get an empty output. What is the most likely reason?

medium

A. The container has no environment variables set

B. The container name is misspelled

C. The format string is missing quotes

D. The Docker daemon is not running

Solution

1. Step 1: Check the format string correctness

   The format string {{.Config.Env}} is valid and properly quoted, so syntax is correct.

2. Step 2: Consider container state and data

   If the container exists and the command runs without error but returns empty, it means no environment variables were set in the container configuration.

3. Final Answer:

   The container has no environment variables set -> Option A

4. Quick Check:

   Empty Env output = no env vars set [OK]

Hint: Empty Env output usually means no env vars set [OK]

Common Mistakes:

• Assuming empty output means syntax error
• Not verifying container name correctness
• Ignoring Docker daemon status errors

5. You want to list all mount points of a container named webapp using docker inspect. Which command will correctly extract this information?

hard

A. docker inspect --format='{{.MountPoints}}' webapp

B. docker inspect --format='{{.Config.Mounts}}' webapp

C. docker inspect --format='{{json .Mounts}}' webapp

D. docker inspect --format='{{.NetworkSettings.Mounts}}' webapp

Solution

1. Step 1: Identify the correct JSON path for mounts

   The .Mounts field contains an array of mount point objects. Using {{json .Mounts}} converts this array to JSON string output.

2. Step 2: Evaluate other options for correctness

   .Config.Mounts and .NetworkSettings.Mounts do not exist. .MountPoints is not a valid field in Docker inspect output.

3. Final Answer:

   docker inspect --format='{{json .Mounts}}' webapp -> Option C

4. Quick Check:

   Use {{json .Mounts}} to get mount points [OK]

Hint: Use {{json .Mounts}} to get mount info in JSON format [OK]

Common Mistakes:

• Using incorrect JSON paths like .Config.Mounts
• Forgetting to use json function for arrays
• Assuming mount info is under NetworkSettings