Docker basics review in Microservices - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Docker in simple terms?

Docker is a tool that lets you package an application and all its parts into a container. This container can run anywhere, making it easy to move and share apps.

beginner

What is a Docker container?

A Docker container is like a small, lightweight box that holds your app and everything it needs to run. It keeps your app isolated from other apps on the same computer.

intermediate

What is the difference between a Docker image and a Docker container?

A Docker image is a blueprint or recipe for creating containers. A container is a running instance made from that image.

intermediate

Why is Docker useful in microservices architecture?

Docker helps by packaging each microservice in its own container. This makes it easy to develop, test, and deploy services independently without conflicts.

beginner

What is a Dockerfile and why do we use it?

A Dockerfile is a simple text file with instructions to build a Docker image. It tells Docker how to set up the app environment step-by-step.

What does a Docker container include?

A The app and all its dependencies

B Only the app code

C Only the operating system

D Only the network settings

A Docker container packages the app along with everything it needs to run, like libraries and dependencies.

Which file is used to build a Docker image?

A README.md

B docker-compose.yml

C config.json

D Dockerfile

A Dockerfile contains instructions to build a Docker image.

How does Docker help with microservices?

A By isolating each service in its own container

B By combining all services into one big app

C By replacing the need for servers

D By removing the need for code

Docker isolates each microservice in its own container, making development and deployment easier.

What is the main difference between a Docker image and a container?

A Image runs the app; container stores the app

B Image is a blueprint; container is a running instance

C Image is bigger than container

D There is no difference

A Docker image is a static blueprint, while a container is a live running instance created from that image.

Which command starts a Docker container?

A docker build

B docker stop

C docker run

D docker pull

The 'docker run' command starts a new container from an image.

Explain how Docker containers help in deploying microservices.

Think about how each microservice runs separately and can be managed on its own.

Describe the role of a Dockerfile in creating Docker images.

Imagine writing a recipe for baking a cake.

Practice

1. What is the main purpose of Docker in microservices architecture?

easy

A. To replace the need for servers entirely

B. To write application code faster

C. To package applications with all dependencies for consistent deployment

D. To monitor network traffic between services

Solution

1. Step 1: Understand Docker's role

   Docker packages applications with their dependencies to ensure they run the same everywhere.

2. Step 2: Compare options

   Only To package applications with all dependencies for consistent deployment describes packaging apps with dependencies; others describe unrelated tasks.

3. Final Answer:

   To package applications with all dependencies for consistent deployment -> Option C

4. Quick Check:

   Docker packages apps = B [OK]

Hint: Docker bundles apps and dependencies for consistent runs [OK]

Common Mistakes:

• Thinking Docker replaces servers
• Confusing Docker with coding tools
• Assuming Docker monitors network

2. Which Docker command is used to create a new image from a Dockerfile?

easy

A. docker run

B. docker start

C. docker push

D. docker build

Solution

1. Step 1: Identify command purpose

   docker build creates an image from a Dockerfile.

2. Step 2: Eliminate other commands

   docker run starts containers, docker start restarts stopped containers, docker push uploads images to a registry.

3. Final Answer:

   docker build -> Option D

4. Quick Check:

   Build = create image [OK]

Hint: Build creates images; run starts containers [OK]

Common Mistakes:

• Using docker run to create images
• Confusing docker start with build
• Thinking docker push creates images

3. Given this Docker command sequence, what happens?

docker build -t myapp .
docker run -d --name app1 myapp

medium

A. Builds an image named myapp and runs it detached as container app1

B. Runs a container named myapp and builds app1 image

C. Builds a container named myapp and runs it interactively

D. Fails because -d and --name cannot be used together

Solution

1. Step 1: Analyze docker build command

   docker build -t myapp . creates an image tagged 'myapp' from current directory.

2. Step 2: Analyze docker run command

   docker run -d --name app1 myapp runs container named 'app1' in detached mode from image 'myapp'.

3. Final Answer:

   Builds an image named myapp and runs it detached as container app1 -> Option A

4. Quick Check:

   Build image then run container detached = A [OK]

Hint: Build tags image; run starts container with name and mode [OK]

Common Mistakes:

• Mixing image and container names
• Thinking -d disables naming
• Confusing build and run order

4. Identify the error in this Docker command:

docker run --name mycontainer -p 8080 myimage

medium

A. Port mapping syntax is incomplete

B. Missing container name

C. Image name is missing

D. Cannot use -p with --name

Solution

1. Step 1: Check port mapping syntax

   -p 8080 is incomplete; it should specify host and container ports like -p 8080:80.

2. Step 2: Verify other parts

   Container name and image name are present; no restriction on using -p with --name.

3. Final Answer:

   Port mapping syntax is incomplete -> Option A

4. Quick Check:

   Port mapping needs host:container format [OK]

Hint: Port mapping needs host:container format [OK]

Common Mistakes:

• Omitting container port in -p
• Assuming image name is missing
• Thinking -p and --name conflict

5. You want to deploy multiple microservices using Docker containers on one host. Which approach best ensures isolation and easy management?

hard

A. Run all microservices inside a single container

B. Use separate containers for each microservice with individual Dockerfiles

C. Install all microservices directly on the host OS without containers

D. Use one container per microservice but share the same network and volumes without isolation

Solution

1. Step 1: Understand container isolation

   Each microservice should run in its own container for isolation and independent management.

2. Step 2: Evaluate options

   Use separate containers for each microservice with individual Dockerfiles uses separate containers with individual Dockerfiles, enabling isolation and scalability. Run all microservices inside a single container mixes services, reducing isolation. Install all microservices directly on the host OS without containers lacks container benefits. Use one container per microservice but share the same network and volumes without isolation shares resources without isolation.

3. Final Answer:

   Use separate containers for each microservice with individual Dockerfiles -> Option B

4. Quick Check:

   Separate containers = isolation + management [OK]

Hint: One container per microservice for isolation and scaling [OK]

Common Mistakes:

• Running all services in one container
• Skipping containers and installing on host
• Sharing networks and volumes without isolation