Inspecting container details in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Inspecting container IP address

You run the command docker inspect -f '{{ .NetworkSettings.IPAddress }}' mycontainer. What is the expected output?

Docker

docker inspect -f '{{ .NetworkSettings.IPAddress }}' mycontainer

A Shows the container's mounted volumes

B Shows the container's image ID

C Shows the IP address assigned to the container named 'mycontainer'

D Shows the container's creation date

💡 Hint

The command uses a Go template to extract network info.

The command uses the Go template to extract the IP address from the container's network settings.

🧠 Conceptual

intermediate

Understanding docker inspect output format

What does the docker inspect command output by default?

A A JSON array with detailed information about the container or image

B A plain text summary of container logs

C A list of running processes inside the container

D The container's resource usage statistics

💡 Hint

Think about the data format used for detailed info.

By default, docker inspect outputs detailed info in JSON format.

❓ Troubleshoot

advanced

Troubleshooting missing container details

You run docker inspect mycontainer but get an error: Error: No such object: mycontainer. What is the most likely cause?

A Docker daemon is not running

B You do not have permission to run docker commands

C The docker inspect command syntax is incorrect

D The container named 'mycontainer' does not exist or is not running

💡 Hint

Check if the container name is correct and exists.

The error means docker cannot find a container with that name or ID.

✅ Best Practice

advanced

Extracting specific container info efficiently

Which command is best to get only the container's mount points using docker inspect?

A docker inspect mycontainer | grep Mounts

B docker inspect -f '{{ json .Mounts }}' mycontainer

C docker inspect -f '{{ .Config.Mounts }}' mycontainer

D docker inspect --format '{{ .HostConfig.Mounts }}' mycontainer

💡 Hint

Use the correct Go template field and format for mounts.

The '.Mounts' field contains mount info; using '{{ json .Mounts }}' outputs it as JSON.

🔀 Workflow

expert

Sequence to find container's exposed ports

Arrange the steps to find the exposed ports of a container named 'webapp' using docker commands.

A 1,3,2,4

B 1,2,3,4

C 3,1,2,4

D 2,1,3,4

💡 Hint

First get details, then extract with template, then interpret.

You first inspect, then extract ports with template, then interpret output.

Practice

1. What does the command docker inspect CONTAINER do?

easy

A. Shows detailed JSON information about the specified container

B. Starts the specified container

C. Deletes the specified container

D. Lists all running containers

Solution

1. Step 1: Understand the command purpose

   The docker inspect command is used to get detailed information about Docker objects like containers.

2. Step 2: Identify the output type

   It returns detailed JSON data about the container's configuration and state.

3. Final Answer:

   Shows detailed JSON information about the specified container -> Option A

4. Quick Check:

   docker inspect = detailed JSON info [OK]

Hint: Remember: inspect means see detailed info [OK]

Common Mistakes:

• Confusing inspect with start or delete commands
• Expecting a simple list instead of JSON output
• Using inspect without specifying a container

2. Which of the following is the correct syntax to get only the container's IP address using docker inspect?

easy

A. docker inspect --format='{{.NetworkSettings.IPAddress}}' CONTAINER

B. docker inspect --ip CONTAINER

C. docker inspect -ip CONTAINER

D. docker inspect --format='{{IPAddress}}' CONTAINER

Solution

1. Step 1: Recall the --format option usage

   The --format flag uses Go templates to extract specific fields from the JSON output.

2. Step 2: Identify the correct template for IP address

   The IP address is under .NetworkSettings.IPAddress, so the correct syntax is {{.NetworkSettings.IPAddress}}.

3. Final Answer:

   docker inspect --format='{{.NetworkSettings.IPAddress}}' CONTAINER -> Option A

4. Quick Check:

   Use --format with correct JSON path [OK]

Hint: Use --format with full JSON path in double braces [OK]

Common Mistakes:

• Using incorrect flags like --ip or -ip
• Missing the dot before NetworkSettings in template
• Not quoting the template string properly

3. Given a container named webapp, what will the command docker inspect --format='{{.State.Status}}' webapp output if the container is running?

medium

A. created

B. paused

C. exited

D. running

Solution

1. Step 1: Understand the .State.Status field

   The .State.Status field shows the current status of the container, such as running, exited, paused, or created.

2. Step 2: Match the container state

   If the container is running, the output will be the string running.

3. Final Answer:

   running -> Option D

4. Quick Check:

   .State.Status = running when container runs [OK]

Hint: Check .State.Status for container current state [OK]

Common Mistakes:

• Confusing status with container name or ID
• Expecting JSON output instead of plain string
• Using wrong field like .Status instead of .State.Status

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

medium

A. The container name is misspelled

B. The format string syntax is incorrect

C. The .Config.Env field does not exist in the container JSON

D. The container is not running

Solution

1. Step 1: Check the format string syntax

   The .Config.Env field is an array, so printing it directly requires proper formatting.

2. Step 2: Identify the syntax error

   Using {{.Config.Env}} tries to print an array directly, which causes a template error. You need to format it, for example with {{range .Config.Env}}{{println .}}{{end}}.

3. Final Answer:

   The format string syntax is incorrect -> Option B

4. Quick Check:

   Arrays need special formatting in --format [OK]

Hint: Arrays need loops in --format templates [OK]

Common Mistakes:

• Assuming all fields print directly without formatting
• Ignoring container name correctness
• Thinking container must be running to inspect

5. You want to list all container names and their IP addresses in a simple format. Which command correctly achieves this?

hard

A. docker ps -q | xargs -n1 docker inspect --format='{{.Name}} {{.NetworkSettings.IPAddress}}'

B. docker ps --format='{{.Name}} {{.NetworkSettings.IPAddress}}'

C. docker inspect --format='{{.Name}} {{.NetworkSettings.IPAddress}}' $(docker ps -q)

D. docker inspect $(docker ps) --format='{{.Name}} {{.NetworkSettings.IPAddress}}'

Solution

1. Step 1: Understand how to get container IDs

   docker ps -q lists container IDs only, which can be passed to docker inspect.

2. Step 2: Use inspect with multiple container IDs and format

   Passing IDs as arguments to docker inspect with --format outputs info for each container. docker inspect --format='{{.Name}} {{.NetworkSettings.IPAddress}}' $(docker ps -q) uses this correctly.

3. Step 3: Check other options for errors

   docker ps -q | xargs -n1 docker inspect --format='{{.Name}} {{.NetworkSettings.IPAddress}}' uses xargs but may break if container names have spaces. docker ps --format='{{.Name}} {{.NetworkSettings.IPAddress}}' is invalid because docker ps does not support .NetworkSettings.IPAddress. docker inspect $(docker ps) --format='{{.Name}} {{.NetworkSettings.IPAddress}}' uses wrong syntax for docker ps.

4. Final Answer:

   docker inspect --format='{{.Name}} {{.NetworkSettings.IPAddress}}' $(docker ps -q) -> Option C

5. Quick Check:

   Use docker inspect with IDs from docker ps -q [OK]

Hint: Use docker inspect with IDs from docker ps -q [OK]

Common Mistakes:

• Trying to get IP from docker ps directly
• Using wrong command substitution syntax
• Not passing container IDs correctly to inspect