Docker deployment in NextJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the Dockerfile to specify the base image for a Next.js app.

NextJS

FROM [1]

Drag options to blanks, or click blank then click option'

Anode:18-alpine

Bpython:3.12

Cubuntu:latest

Dnginx:alpine

Attempts:

3 left

💡 Hint

Common Mistakes

Using a Python or Ubuntu image which lacks Node.js.

Using Nginx as base image which is for serving static files only.

The base image node:18-alpine is a lightweight Node.js image suitable for Next.js apps.

2fill in blank

medium

Complete the Dockerfile command to copy package.json and package-lock.json files.

NextJS

COPY [1] ./

Drag options to blanks, or click blank then click option'

Anode_modules/

Bsrc/

Cpackage*.json

Dpublic/

Attempts:

3 left

💡 Hint

Common Mistakes

Copying the entire src folder instead of package files.

Copying node_modules which should be installed inside the container.

Using package*.json copies both package.json and package-lock.json files needed for installing dependencies.

3fill in blank

hard

Fix the error in the Dockerfile command to install dependencies.

NextJS

RUN npm [1]

Drag options to blanks, or click blank then click option'

Arun

Bstart

Cbuild

Dinstall

Attempts:

3 left

💡 Hint

Common Mistakes

Using npm start which runs the app instead of installing.

Using npm build which is not a valid npm command.

The npm install command installs all dependencies listed in package.json.

4fill in blank

hard

Fill both blanks to expose the correct port and set the command to start the Next.js app.

NextJS

EXPOSE [1]
CMD ["npm", "[2]"]

Drag options to blanks, or click blank then click option'

A3000

Bstart

Cbuild

D8080

Attempts:

3 left

💡 Hint

Common Mistakes

Exposing port 8080 which is not default for Next.js.

Using npm build as the start command.

Next.js apps by default run on port 3000, and npm start runs the production server.

5fill in blank

hard

Fill all three blanks to create a Docker Compose service for the Next.js app with build context, port mapping, and environment variable.

NextJS

services:
  web:
    build: [1]
    ports:
      - "[2]:3000"
    environment:
      - NODE_ENV=[3]

Drag options to blanks, or click blank then click option'

A"."

B3000

Cproduction

Ddevelopment

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong build context path.

Mapping wrong ports or setting NODE_ENV to development in production.

The build context is the current directory ".", port 3000 is mapped, and NODE_ENV is set to production for deployment.

Practice

1. What is the main purpose of using Docker for deploying a Next.js application?

easy

A. To write the Next.js code faster

B. To package the app with all dependencies for consistent running anywhere

C. To replace the need for React in the app

D. To automatically generate CSS styles

Solution

1. Step 1: Understand Docker's role

   Docker packages an app with its environment so it runs the same on any machine.

2. Step 2: Relate to Next.js deployment

   This packaging ensures the Next.js app and its dependencies work consistently everywhere.

3. Final Answer:

   To package the app with all dependencies for consistent running anywhere -> Option B

4. Quick Check:

   Docker ensures consistent app environment = A [OK]

Hint: Docker packages app and dependencies for consistent deployment [OK]

Common Mistakes:

• Thinking Docker speeds up coding
• Confusing Docker with React features
• Assuming Docker styles the app automatically

2. Which of the following is the correct first line in a Dockerfile for deploying a Next.js app using Node.js 18?

easy

A. FROM node:18-alpine

B. RUN node install 18

C. COPY node:18 /app

D. START node version 18

Solution

1. Step 1: Identify Dockerfile base image syntax

   The Dockerfile starts with FROM followed by the base image name and tag.

2. Step 2: Match Node.js 18 base image

   Node official images use 'node:18-alpine' for a lightweight Node 18 environment.

3. Final Answer:

   FROM node:18-alpine -> Option A

4. Quick Check:

   Dockerfile base image starts with FROM = B [OK]

Hint: Dockerfile starts with FROM and image name [OK]

Common Mistakes:

• Using RUN instead of FROM for base image
• Trying to COPY node version as a command
• Using START which is not a Dockerfile command

3. Given this Dockerfile snippet for Next.js deployment:

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

What happens when you run this Docker image?

medium

A. The app builds and starts serving on default port

B. The app installs dependencies but never builds

C. The app builds but fails to start

D. The Dockerfile causes a syntax error

Solution

1. Step 1: Analyze Dockerfile commands

   It sets working directory, copies package.json, installs dependencies, copies all files, builds app, then starts it.

2. Step 2: Understand CMD effect

   CMD runs 'npm start' which serves the built Next.js app on default port 3000.

3. Final Answer:

   The app builds and starts serving on default port -> Option A

4. Quick Check:

   Build then start with npm = C [OK]

Hint: RUN builds, CMD starts app in Dockerfile [OK]

Common Mistakes:

• Assuming build step is missing
• Thinking CMD does not start the app
• Believing Dockerfile syntax is wrong here

4. You wrote this Dockerfile for your Next.js app but get an error when running the container:

FROM node:18-alpine
WORKDIR /app
COPY . .
RUN npm install
RUN npm run build
CMD npm start

What is the likely cause of the error?

medium

A. npm run build should be replaced with npm build

B. COPY command should come after RUN npm install

C. WORKDIR must be set after RUN commands

D. CMD syntax is incorrect; it should be an array

Solution

1. Step 1: Check CMD syntax

   CMD should be an array like ["npm", "start"] to run correctly in Docker.

2. Step 2: Verify other commands

   COPY before npm install is fine; WORKDIR before RUN is correct; npm run build is valid.

3. Final Answer:

   CMD syntax is incorrect; it should be an array -> Option D

4. Quick Check:

   CMD needs array syntax = A [OK]

Hint: Use array syntax for CMD in Dockerfile [OK]

Common Mistakes:

• Writing CMD as a string instead of array
• Moving COPY after npm install unnecessarily
• Changing npm run build to npm build incorrectly

5. You want to deploy a Next.js app with Docker and ensure it listens on port 8080 instead of the default 3000. Which change should you make in your Dockerfile and app start command?

hard

A. Modify Dockerfile to FROM node:8080 and keep app default

B. Change CMD to ["npm", "start", "--port", "8080"] without app changes

C. Set ENV PORT=8080 and run CMD ["npm", "start"] with app configured to use process.env.PORT

D. Expose port 8080 but keep app listening on 3000

Solution

1. Step 1: Set environment variable for port

   Use ENV PORT=8080 in Dockerfile so app can read the port from environment.

2. Step 2: Ensure app uses process.env.PORT

   Next.js app must listen on process.env.PORT to respect Docker port setting.

3. Final Answer:

   Set ENV PORT=8080 and run CMD ["npm", "start"] with app configured to use process.env.PORT -> Option C

4. Quick Check:

   Use ENV and app reads process.env.PORT = D [OK]

Hint: Set ENV PORT and app reads process.env.PORT [OK]

Common Mistakes:

• Changing base image to node:8080 (invalid)
• Exposing port without changing app port
• Passing port as npm start argument without app support