Dockerfile for microservices - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this Docker build command?

Given the following Dockerfile for a Node.js microservice, what will be the output when running docker build -t myservice .?

Microservices

FROM node:18-alpine
WORKDIR /app
COPY package.json .
RUN npm install
COPY . .
CMD ["node", "server.js"]

A Successfully built image with tag 'myservice' and no errors

B Error: 'package.json' not found during COPY step

C Error: npm install failed due to missing package.json

D Build hangs indefinitely at RUN npm install

💡 Hint

Check if the Dockerfile copies package.json before running npm install.

The Dockerfile copies package.json before running npm install, so dependencies install correctly. The build completes successfully with the image tagged 'myservice'.

❓ Configuration

intermediate

Which Dockerfile snippet correctly sets environment variables for a microservice?

Choose the Dockerfile snippet that correctly sets environment variables PORT to 8080 and NODE_ENV to production.

A ENV PORT 8080 NODE_ENV production

B ENV PORT:8080 NODE_ENV:production

C ENV PORT=8080 NODE_ENV=production

D ENV PORT=8080; NODE_ENV=production

💡 Hint

Look for the correct syntax to set multiple environment variables in one ENV instruction.

The correct syntax uses ENV VAR=value pairs separated by spaces. Option C correctly sets both variables.

❓ Troubleshoot

advanced

Why does this Dockerfile cause a large image size?

Consider this Dockerfile for a Python microservice:

FROM python:3.12
WORKDIR /app
COPY . .
RUN pip install -r requirements.txt
CMD ["python", "app.py"]

Why might this Docker image be larger than necessary?

A It does not specify a user, causing permission issues

B It uses an outdated Python base image

C It runs pip install without caching dependencies

D It copies all files including unnecessary ones like tests and docs

💡 Hint

Think about what files get included in the image when using COPY . ..

Copying the entire context includes unnecessary files like tests and documentation, increasing image size. Using a .dockerignore file can exclude these.

🔀 Workflow

advanced

What is the correct order of Dockerfile instructions for efficient caching?

Arrange these Dockerfile instructions in the best order to optimize Docker layer caching for a Node.js microservice:

A 1,2,3,4

B 2,1,3,4

C 3,1,2,4

D 1,3,2,4

💡 Hint

Think about which files change most often and how Docker caches layers.

Copying package.json and running npm install first allows Docker to cache dependencies. Copying the rest of the code later avoids reinstalling packages unnecessarily.

✅ Best Practice

expert

Which Dockerfile practice improves security for microservices?

Which option shows the best Dockerfile practice to improve security by avoiding running the container as root?

A USER node

B RUN adduser appuser && USER appuser

C USER 1000

D RUN chmod 777 /app && USER root

💡 Hint

Consider creating a non-root user and switching to it.

Option B creates a new user and switches to it, reducing security risks. Option B uses an existing user but may not exist in all images. Option B uses a numeric ID without context. Option B keeps root user with insecure permissions.