Docker basics review in Microservices - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Docker Image Layers

Which statement best describes how Docker image layers work?

A Layers are stacked and share common files, so changes create new layers without duplicating unchanged data.

B Each layer is a complete copy of the entire image, making images large but independent.

C Docker images do not use layers; each image is a single file containing all data.

D Layers are only used during build time and discarded after the container starts.

💡 Hint

Think about how Docker saves space and speeds up builds by reusing parts.

Docker images are built in layers. Each layer represents changes from the previous one. This allows sharing common parts between images and efficient storage.

❓ Architecture

intermediate

Docker Container Networking Basics

In a typical Docker setup, how do containers communicate with each other on the same host?

A Containers use the host's network stack directly without isolation.

B Containers cannot communicate with each other unless exposed to the internet.

C Each container has a unique public IP address assigned by Docker for direct communication.

D Containers communicate over a virtual bridge network created by Docker, allowing isolated but connected communication.

💡 Hint

Think about how Docker isolates containers but still allows them to talk inside the same machine.

Docker creates a virtual bridge network on the host. Containers connect to this bridge and can communicate using internal IPs, isolated from the host network.

❓ scaling

advanced

Scaling Microservices with Docker Containers

You have a microservice running in a Docker container that needs to handle increased traffic. Which approach best supports scaling this service?

A Run the container in privileged mode to allow it to use more host resources automatically.

B Run multiple instances of the container across different hosts and use a load balancer to distribute traffic.

C Increase the CPU and memory limits of the single container to handle more requests.

D Modify the container image to include all dependencies and restart it to refresh resources.

💡 Hint

Think about horizontal scaling and distributing load.

Scaling microservices is best done by running multiple container instances and balancing traffic among them. This approach improves availability and handles more users.

❓ tradeoff

advanced

Tradeoffs of Using Docker Volumes vs Bind Mounts

When persisting data for Docker containers, what is a key tradeoff between using Docker volumes and bind mounts?

A Bind mounts automatically backup data; volumes require manual backup.

B Bind mounts are encrypted by default; volumes are stored in plain text on the host.

C Volumes are managed by Docker and offer better portability; bind mounts directly map host files but can cause permission issues.

D Volumes cannot be shared between containers; bind mounts can be shared easily.

💡 Hint

Consider management, portability, and permission differences.

Docker volumes are stored in Docker-managed locations and are portable across hosts. Bind mounts link directly to host files or directories, which can cause permission and portability challenges.

❓ estimation

expert

Estimating Docker Container Resource Needs

You plan to deploy 100 Docker containers running a CPU-intensive microservice on a server with 64 CPU cores and 256 GB RAM. Each container requires 0.5 CPU cores and 2 GB RAM. What is the minimum number of such servers needed to run all containers without resource contention?

A 1 server

B 4 servers

C 3 servers

D 2 servers

💡 Hint

Calculate total CPU and RAM needed, then divide by server capacity.

Total CPU needed: 100 containers * 0.5 cores = 50 cores.
Total RAM needed: 100 containers * 2 GB = 200 GB.
One server has 64 cores (>50) and 256 GB RAM (>200 GB), so the minimum number of servers needed is 1.

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