Lesson 08

ENTRYPOINT, CMD, and signals

Use exec-form commands and keep startup wrappers signal-safe so containers stop gracefully.

entrypoint
cmd
signals

Good Code

Dockerfile

FROM node:22-alpine

WORKDIR /app
COPY package.json package-lock.json ./
RUN npm ci --omit=dev
COPY server.js ./server.js

# Exec form lets node receive Docker stop signals directly.
ENTRYPOINT ["node"]
CMD ["server.js"]

Bad Code

Dockerfile

FROM node:22-alpine

WORKDIR /app
COPY . .
RUN npm install

# Shell form wraps the app in a shell, making stop signals harder to handle.
CMD npm start

Review Notes

What to review

Good Code

The good version uses exec form, so the application process receives termination signals directly.

Bad Code

The bad version uses shell form. The shell can become PID 1 and make signal forwarding and graceful shutdown less predictable.

Takeaways

The process started by Docker should receive signals directly and shut down predictably.