Docker inspect for detailed info - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Inspecting container network settings

You run the command docker inspect my_container and want to find the IP address assigned to the container. Which command filters the IP address correctly?

A docker inspect -f '{{ .Config.IPAddress }}' my_container

B docker inspect -f '{{ .Network.IPAddress }}' my_container

C docker inspect -f '{{ .NetworkSettings.IPAddress }}' my_container

D docker inspect -f '{{ .HostConfig.IPAddress }}' my_container

💡 Hint

Look inside the NetworkSettings section for IP details.

The IP address of a Docker container is stored under NetworkSettings.IPAddress. The other options point to incorrect or non-existent fields.

💻 Command Output

intermediate

Finding container mount points

Which docker inspect command shows the source paths of volumes mounted inside a container named webapp?

A docker inspect -f '{{ range .Mounts }}{{ .Source }} {{ end }}' webapp

B docker inspect -f '{{ .Config.Mounts }}' webapp

C docker inspect -f '{{ .HostConfig.Binds }}' webapp

D docker inspect -f '{{ .Volumes }}' webapp

💡 Hint

Mount points are listed under the Mounts array.

The Mounts array contains details about volume mounts including their source paths. The other fields do not provide this information directly.

❓ Troubleshoot

advanced

Diagnosing missing environment variables

You inspect a container but notice the environment variables you set are missing. Which field in the docker inspect output should you check to verify environment variables?

A Config.Env

B HostConfig.Env

C NetworkSettings.Env

D Mounts.Env

💡 Hint

Environment variables are part of the container configuration.

Environment variables are stored in the Config.Env field. Other fields do not contain environment variable information.

🧠 Conceptual

advanced

Understanding Docker inspect output format

What is the default output format of the docker inspect command?

A Plain text summary

B JSON formatted detailed information

C YAML formatted data

D XML formatted data

💡 Hint

Think about the data format used for structured output in Docker CLI.

The default output of docker inspect is JSON, which provides detailed structured information about containers or images.

✅ Best Practice

expert

Efficiently extracting container creation time

You want to get only the creation time of a container named dbserver using docker inspect. Which command is the most efficient and correct?

A docker inspect -f '{{ .State.Created }}' dbserver

B docker inspect dbserver | grep Created

C docker inspect -f '{{ .Config.Created }}' dbserver

D docker inspect -f '{{ .Created }}' dbserver

💡 Hint

Creation time is a top-level field in the inspect JSON.

The Created field is at the top level of the inspect output. Using the Go template with -f flag to extract {{ .Created }} is efficient and precise.

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