Docker engine and runtime - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Identify Docker Engine Version Output

What is the output of the command docker version --format '{{.Server.Version}}' when Docker Engine version 24.0.2 is installed?

Docker

docker version --format '{{.Server.Version}}'

A 24.0.2

B Client: 24.0.2

C Version: 24.0.2

D Docker Engine 24.0.2

💡 Hint

The --format option outputs only the specified field without extra text.

The command outputs only the server version string exactly as '24.0.2' without any prefix or label.

🧠 Conceptual

intermediate

Docker Runtime Default Behavior

Which statement correctly describes the default runtime used by Docker Engine when running containers?

A Docker uses the Kata Containers runtime by default for enhanced security.

B Docker uses the runc runtime by default to create and run containers.

C Docker uses the cri-o runtime by default for container orchestration.

D Docker uses the containerd runtime by default to run containers.

💡 Hint

Think about the low-level runtime that Docker calls to create containers.

Docker Engine uses runc as the default runtime to create and run containers. containerd is a daemon Docker uses internally, but runc is the runtime that actually runs containers.

❓ Troubleshoot

advanced

Diagnose Docker Engine Startup Failure

A user reports that Docker Engine fails to start with the error message: failed to start daemon: Error initializing network controller: Error creating default "bridge" network: failed to allocate gateway (172.17.0.1): Address already in use. What is the most likely cause?

A Another process is already using the default Docker bridge network IP address range.

B Docker daemon configuration file is missing the bridge network settings.

C Docker Engine version is incompatible with the host kernel version.

D The Docker socket file has incorrect permissions.

💡 Hint

The error mentions 'Address already in use' for the gateway IP.

The error indicates the default Docker bridge network IP range overlaps with an existing network on the host, causing a conflict.

🔀 Workflow

advanced

Sequence to Change Docker Runtime

What is the correct sequence of steps to change the default Docker runtime from runc to nvidia runtime on a Linux host?

A 2,1,3,4

B 1,3,2,4

C 3,1,2,4

D 1,2,3,4

💡 Hint

Configuration changes require daemon restart before verification.

First, configure the daemon.json file, then restart Docker to apply changes, verify the runtime is listed, and finally run containers using the new runtime.

✅ Best Practice

expert

Best Practice for Docker Engine Security Hardening

Which of the following is the best practice to minimize security risks when running Docker Engine in production?

A Run Docker Engine as root user to ensure full access to system resources.

B Disable Docker Content Trust to speed up image pulls.

C Use user namespaces to map container users to non-root host users.

D Allow all containers to run with privileged mode for compatibility.

💡 Hint

Think about isolating container privileges from the host system.

Using user namespaces maps container root users to non-root users on the host, reducing risk if a container is compromised.