Docker containerization in NestJS - Step-by-Step Execution

Concept Flow - Docker containerization

Write Dockerfile

↓

Build Docker Image

↓

Run Docker Container

↓

NestJS App Runs Inside Container

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Access App via Port Mapping

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Container Stops or Restart

This flow shows how a NestJS app is containerized: writing a Dockerfile, building an image, running a container, and accessing the app.

Execution Sample

NestJS

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

This Dockerfile sets up a NestJS app environment, installs dependencies, copies code, builds the app, and starts the app in production mode.

Execution Table

Step	Action	Details	Result
1	Read Dockerfile	FROM node:18-alpine	Base image set to Node 18 Alpine
2	Set working directory	WORKDIR /app	Working directory inside container is /app
3	Copy package files	COPY package*.json ./	package.json and package-lock.json copied
4	Install dependencies	RUN npm install	Node modules installed inside container
5	Copy app code	COPY . .	All app files copied into /app
6	Build app	RUN npm run build	NestJS app compiled to /app/dist
7	Set start command	CMD ["npm", "run", "start:prod"]	Container will run NestJS app in production
8	Build image	docker build -t nestjs-app .	Docker image 'nestjs-app' created
9	Run container	docker run -p 3000:3000 nestjs-app	Container runs, app accessible on localhost:3000
10	Access app	Open browser at http://localhost:3000	NestJS app responds to requests
11	Stop container	Ctrl+C or docker stop	Container stops running

💡 Container stops when user stops it or system shuts down

Variable Tracker

Variable	Start	After Step 3	After Step 5	After Step 9	Final
Docker Image	None	Base image set	App code added	Image built	Image ready to run
Container	None	None	None	Running with app	Stopped or running

Key Moments - 3 Insights

Why do we copy package.json files before running npm install?

Copying package.json first allows Docker to cache npm install step if dependencies don't change, speeding up rebuilds (see execution_table step 3 and 4).

What does the CMD instruction do in the Dockerfile?

CMD sets the command to run when the container starts, here it runs the NestJS app in production mode (see execution_table step 7).

Why map port 3000 in docker run command?

Port mapping (-p 3000:3000) connects container's port 3000 to host's port 3000, so you can access the app from your browser (see execution_table step 9 and 10).

Visual Quiz - 3 Questions

Look at the execution table, at which step is the NestJS app code copied into the Docker image?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

Check the 'Action' and 'Details' columns for copying app code.

At which step does the container start running the NestJS app?

A Step 9

B Step 7

C Step 8

D Step 6

💡 Hint

Look for 'Run container' action in the execution table.

If you forget to map port 3000 in the docker run command, what happens?

A You can still access the app on localhost:3000

B You cannot access the app from your host machine

C The container will not start

D The app runs on a different port automatically

💡 Hint

Refer to step 9 and 10 about port mapping and app access.

Concept Snapshot

Docker containerization for NestJS:
- Write a Dockerfile with base image, copy files, install dependencies
- Build image with 'docker build'
- Run container with port mapping 'docker run -p host:container'
- Container runs NestJS app isolated
- Access app via mapped port on host
- Stop container when done

Full Transcript

Docker containerization for a NestJS app involves creating a Dockerfile that starts from a Node.js base image, sets a working directory, copies package files, installs dependencies, copies the app code, and sets the command to run the app. The Docker image is built using 'docker build', then run with 'docker run' including port mapping to access the app from the host machine. The container runs the NestJS app isolated from the host environment. You can access the app in a browser via the mapped port. The container stops when you stop it manually or the system shuts down.