Docker engine and runtime - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Docker Engine?

Docker Engine is the core software that builds, runs, and manages containers on your computer. It acts like a mini factory that creates and runs containerized apps.

beginner

What are the main components of Docker Engine?

The main parts are: 1) Docker Daemon (runs in background and manages containers), 2) Docker CLI (the command tool you use), and 3) REST API (lets other programs talk to Docker).

beginner

What does the Docker runtime do?

The Docker runtime is the part that actually starts and stops containers. It uses container technology to isolate apps so they run the same everywhere.

intermediate

How does Docker Engine use container technology?

Docker Engine uses OS features like namespaces and cgroups to create isolated spaces called containers. This keeps apps separate and controls their resource use.

beginner

Why is Docker Engine important for DevOps?

Docker Engine helps DevOps by making app deployment fast, consistent, and easy to manage. It lets teams build once and run anywhere without surprises.

What is the role of the Docker Daemon?

A It compiles Dockerfiles into code.

B It builds the Docker CLI interface.

C It manages containers and listens for Docker commands.

D It stores Docker images in the cloud.

The Docker Daemon runs in the background and manages container lifecycle and resources.

Which component do you use to run Docker commands?

A Docker CLI

B Docker Daemon

C Docker Hub

D Docker Compose

The Docker CLI is the command-line tool you use to interact with Docker Engine.

What technology does Docker use to isolate containers?

A Virtual machines

B Namespaces and cgroups

C Cloud servers

D Kubernetes pods

Docker uses OS features like namespaces and cgroups to isolate containers.

What happens when you run a container with Docker runtime?

A Docker compiles the app into machine code.

B Docker uploads the app to the cloud.

C Docker deletes the app from your system.

D Docker creates an isolated environment and starts the app inside it.

The Docker runtime creates an isolated container and runs the app inside it.

Why is Docker Engine useful in DevOps?

A It ensures apps run the same on any machine.

B It replaces all servers with virtual machines.

C It automatically writes code for developers.

D It only works on Windows systems.

Docker Engine provides consistent environments so apps behave the same everywhere.

Explain what Docker Engine is and how it works to run containers.

Think of Docker Engine as the engine of a car that powers container apps.

Describe the main components of Docker Engine and their functions.

Imagine the Docker CLI as the driver, the Daemon as the engine, and the API as the communication system.

Practice

1. What is the primary role of the Docker engine in container management?

easy

A. It manages and controls containers on your system.

B. It builds the Linux kernel for container support.

C. It acts as a cloud service for container hosting.

D. It provides a graphical interface for container design.

Solution

1. Step 1: Understand Docker engine's function

   The Docker engine is the main software that manages containers, including building, running, and controlling them.

2. Step 2: Compare options with this role

   Only It manages and controls containers on your system. correctly states that Docker engine manages and controls containers on your system.

3. Final Answer:

   It manages and controls containers on your system. -> Option A

4. Quick Check:

   Docker engine = container management [OK]

Hint: Docker engine controls containers, not builds kernels or UI [OK]

Common Mistakes:

• Confusing Docker engine with cloud services
• Thinking Docker engine builds the OS kernel
• Assuming Docker engine is a GUI tool

2. Which of the following is the correct command to check the Docker engine version?

easy

A. docker version

B. docker check-version

C. docker show version

D. docker engine info

Solution

1. Step 1: Recall Docker command syntax for version

   The correct command to check Docker engine version is docker version.

2. Step 2: Validate other options

   Options A, B, and C are not valid Docker commands for checking version.

3. Final Answer:

   docker version -> Option A

4. Quick Check:

   Check version command = docker version [OK]

Hint: Use 'docker version' to see engine version quickly [OK]

Common Mistakes:

• Using incorrect command names like 'docker check-version'
• Confusing 'docker info' with version command
• Trying 'docker engine info' which is invalid

3. What will be the output of the command docker ps when no containers are running?

medium

A. Displays an error saying no containers found

B. Lists all containers including stopped ones

C. Shows an empty list with only headers

D. Starts a new container automatically

Solution

1. Step 1: Understand what 'docker ps' shows

   The command docker ps lists running containers only, showing headers even if none are running.

2. Step 2: Analyze output when no containers run

   When no containers run, it shows an empty list with column headers but no container entries.

3. Final Answer:

   Shows an empty list with only headers -> Option C

4. Quick Check:

   docker ps with no containers = empty list [OK]

Hint: 'docker ps' shows running containers; empty if none run [OK]

Common Mistakes:

• Thinking it lists stopped containers too
• Expecting an error message when no containers run
• Assuming it starts containers automatically

4. You run docker run -d nginx but get an error: "Cannot connect to the Docker daemon." What is the likely cause?

medium

A. The container is already running.

B. The nginx image does not exist on Docker Hub.

C. The command syntax is incorrect.

D. Docker daemon is not running on the system.

Solution

1. Step 1: Understand the error message

   "Cannot connect to the Docker daemon" means the Docker engine service (daemon) is not running or accessible.

2. Step 2: Check other options

   Image absence or syntax errors cause different errors; container running does not cause daemon connection errors.

3. Final Answer:

   Docker daemon is not running on the system. -> Option D

4. Quick Check:

   Daemon connection error = daemon not running [OK]

Hint: Daemon errors mean Docker service is stopped or unreachable [OK]

Common Mistakes:

• Assuming image absence causes daemon errors
• Blaming command syntax for daemon connection issues
• Thinking container running causes this error

5. You want to run a container using a runtime other than the default Docker runtime. Which command option lets you specify the runtime?

hard

A. docker run --use-runtime=<runtime_name> <image>

B. docker run --runtime=<runtime_name> <image>

C. docker run --engine=<runtime_name> <image>

D. docker run --container-runtime=<runtime_name> <image>

Solution

1. Step 1: Recall Docker run options for runtime

   The correct option to specify a runtime is --runtime followed by the runtime name.

2. Step 2: Verify other options

   Options A, B, and D are not valid Docker CLI options for runtime selection.

3. Final Answer:

   docker run --runtime=<runtime_name> <image> -> Option B

4. Quick Check:

   Specify runtime with --runtime option [OK]

Hint: Use '--runtime' option to select container runtime [OK]

Common Mistakes:

• Using incorrect flags like --engine or --use-runtime
• Confusing runtime with engine options
• Omitting the runtime option entirely