Challenge - Dockerfile

Write a Dockerfile for a web application.

Challenge: a production-ready Dockerfile

In this challenge you'll combine all the good practices for a Node.js API in a single Dockerfile:

A small base image with a pinned version
Cache-friendly order (package*.json first)
Only production dependencies
A non-root user
A start command in exec form

FROM node:20-alpine
ENV NODE_ENV=production
WORKDIR /app
COPY package*.json ./
RUN npm ci --omit=dev
COPY --chown=node:node . .
USER node
EXPOSE 3000
CMD ["node", "server.js"]

Exercise Write the Dockerfile

Write the Dockerfile from the card: node:20-alpine; ENV NODE_ENV=production; WORKDIR /app; copy package*.json and run npm ci --omit=dev; copy the code with --chown=node:node; USER node; EXPOSE 3000; node server.js in exec form.

Show example solution

FROM node:20-alpine
ENV NODE_ENV=production
WORKDIR /app
COPY package*.json ./
RUN npm ci --omit=dev
COPY --chown=node:node . .
USER node
EXPOSE 3000
CMD ["node", "server.js"]

Exercise Add a .dockerignore

Write a .dockerignore for the same project: exclude node_modules, .git, .env, npm-debug.log and Dockerfile.

Show example solution

node_modules
.git
.env
npm-debug.log
Dockerfile

Test yourself

In the Dockerfile above, which step reruns if only server.js changes?
- Only FROM
- None
- COPY --chown=node:node . . and after
- All of them including npm ci
Show answer

COPY --chown=node:node . . and after — Since package*.json didn't change, npm ci comes from the cache.
Install only the production dependencies.
```
RUN npm ci ____
```
Show answer
```
RUN npm ci --omit=dev
```
Match the practices with their purposes.

node:20-alpine

Small, pinned base
package*.json first

Cache
USER node

Least privilege
["node", "server.js"]

Signal handling

Next lesson: Challenge - Build and run

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