Inspecting container network settings in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What command shows detailed network settings of a running Docker container?

Use docker inspect <container_id_or_name> to see detailed information including network settings.

beginner

What key in the docker inspect output contains network information?

The NetworkSettings key holds IP address, gateway, ports, and network mode details.

beginner

How can you find the IP address of a Docker container?

Look under NetworkSettings.Networks[<network_name>].IPAddress in the docker inspect output.

beginner

What does the docker network ls command do?

It lists all Docker networks available on your system.

intermediate

How do you inspect a specific Docker network's details?

Use docker network inspect <network_name> to see connected containers and settings.

Which command shows the IP address of a Docker container?

A docker logs <container>

B docker inspect <container>

C docker run

D docker ps

The docker inspect command shows detailed info including the IP address.

Where in the inspect output can you find port mappings?

A NetworkSettings.Ports

B Config.Env

C Mounts

D State.Status

Port mappings are listed under NetworkSettings.Ports.

What does docker network ls display?

A List of running containers

B List of volumes

C List of images

D List of Docker networks

It lists all Docker networks on the system.

How to see which containers are connected to a Docker network?

A docker network inspect <network>

B docker ps

C docker container ls

D docker volume ls

Inspecting a network shows connected containers.

Which key in docker inspect output shows the network mode?

A State.Running

B Config.Cmd

C HostConfig.NetworkMode

D Mounts

Network mode is under HostConfig.NetworkMode.

Explain how to find the IP address and port mappings of a Docker container.

Think about the detailed info shown by docker inspect.

Describe how to list Docker networks and inspect a specific network's connected containers.

Focus on Docker network commands.

Practice

1. Which Docker command shows detailed information about a specific network, including connected containers?

easy

A. docker ps

B. docker container inspect <container_id>

C. docker network inspect <network_name>

D. docker network ls

Solution

1. Step 1: Understand the purpose of docker network inspect

   This command provides detailed info about a Docker network, including which containers are connected.

2. Step 2: Compare with other commands

   docker container inspect shows container details, docker ps lists running containers, and docker network ls lists networks without details.

3. Final Answer:

   docker network inspect <network_name> -> Option C

4. Quick Check:

   Network details = docker network inspect [OK]

Hint: Use docker network inspect for network details [OK]

Common Mistakes:

• Confusing container inspect with network inspect
• Using docker ps to get network info
• Using docker network ls for detailed info

2. Which of the following commands correctly shows the IP address of a running container named webapp using docker container inspect with formatting?

easy

A. docker container inspect --format '{{.NetworkSettings.IPAddress}}' webapp

B. docker container inspect --format '{{.Network.IP}}' webapp

C. docker inspect --format '{{.NetworkSettings.IP}}' webapp

D. docker container inspect --format '{{.IPAddress}}' webapp

Solution

1. Step 1: Identify correct JSON path for IP address

   The IP address is under .NetworkSettings.IPAddress in container inspect output.

2. Step 2: Check command syntax

   docker container inspect --format '{{.NetworkSettings.IPAddress}}' webapp uses correct command and format string. Others use incorrect paths or omit 'container'.

3. Final Answer:

   docker container inspect --format '{{.NetworkSettings.IPAddress}}' webapp -> Option A

4. Quick Check:

   IP address path = .NetworkSettings.IPAddress [OK]

Hint: Use .NetworkSettings.IPAddress to get container IP [OK]

Common Mistakes:

• Using wrong JSON path like .Network.IP
• Omitting 'container' in the command
• Using '{{.IPAddress}}' which is invalid

3. Given a container named db connected to a network backend_net, what will the command docker network inspect backend_net show about the container?

medium

A. It lists the container ID and its IPv4 address inside the network.

B. It shows only the container name without IP details.

C. It shows the container's CPU and memory usage.

D. It shows the container's logs.

Solution

1. Step 1: Understand output of docker network inspect

   This command shows network details including connected containers with their IDs and IP addresses.

2. Step 2: Eliminate incorrect options

   It does not show CPU/memory usage or logs, and it includes IP info, not just names.

3. Final Answer:

   It lists the container ID and its IPv4 address inside the network. -> Option A

4. Quick Check:

   Network inspect shows container IDs and IPs [OK]

Hint: Network inspect shows container IDs and IPs connected [OK]

Common Mistakes:

• Expecting resource usage info from network inspect
• Thinking it shows logs
• Assuming only container names appear

4. You run docker container inspect --format '{{.NetworkSettings.IPAddress}}' myapp but get an empty output. What is the most likely reason?

medium

A. The container myapp is not connected to the default bridge network.

B. Docker daemon is not running.

C. The command syntax is incorrect.

D. The container myapp is stopped.

Solution

1. Step 1: Understand when IPAddress is empty

   If a container is stopped, it has no active network interface, so IPAddress is empty.

2. Step 2: Check other options

   Not connected to default network still shows IP if connected elsewhere; syntax is correct; daemon not running causes errors, not empty output.

3. Final Answer:

   The container myapp is stopped. -> Option D

4. Quick Check:

   Stopped container IP is empty [OK]

Hint: Empty IP means container likely stopped [OK]

Common Mistakes:

• Assuming wrong syntax causes empty output
• Thinking network choice causes empty IP
• Ignoring container running state

5. You want to list all containers connected to a custom network mynet and show their names and IP addresses in a simple table. Which approach is best?

hard

A. Run docker ps and guess which containers belong to mynet.

B. Use docker network inspect mynet and parse the JSON to extract container names and IPs.

C. Use docker container inspect --format '{{.Name}} {{.NetworkSettings.IPAddress}}' on all containers and filter manually.

D. Restart Docker daemon to refresh network info.

Solution

1. Step 1: Identify command that shows network container info

   docker network inspect mynet lists all containers connected with their IPs.

2. Step 2: Understand why other options are less effective

   docker ps doesn't show network info; inspecting all containers is manual and error-prone; restarting daemon is unrelated.

3. Final Answer:

   Use docker network inspect mynet and parse the JSON to extract container names and IPs. -> Option B

4. Quick Check:

   Network inspect shows connected containers best [OK]

Hint: Use docker network inspect to get connected containers easily [OK]

Common Mistakes:

• Using docker ps to find network info
• Inspecting containers individually without filtering
• Restarting daemon unnecessarily