We are used to see code examples where folks start their app using CMD 'npm start'. This is a bad practice. The npm binary will not forward signals to your app which prevents graceful shutdown (see [/sections/docker/graceful-shutdown.md]). If you are using child-processes they won’t be cleaned up correctly in case of unexpected shutdown, leaving zombie processes on your host. npm start also results in having an extra process for no benefit. To start you app use CMD ['node','server.js']. If your app spawns child-processes also use TINI as an entrypoint.
FROM node:12-slim AS build
WORKDIR /usr/src/app
COPY package.json package-lock.json ./
RUN npm ci --production && npm clean cache --force
CMD ["node", "server.js"]FROM node:12-slim AS build
# Add Tini if using child-processes
ENV TINI_VERSION v0.19.0
ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini /tini
RUN chmod +x /tini
WORKDIR /usr/src/app
COPY package.json package-lock.json ./
RUN npm ci --production && npm clean cache --force
ENTRYPOINT ["/tini", "--"]
CMD ["node", "server.js"]Using npm start
FROM node:12-slim AS build
WORKDIR /usr/src/app
COPY package.json package-lock.json ./
RUN npm ci --production && npm cache clean --force
# don’t do that!
CMD "npm start"Using node in a single string will start a bash/ash shell process to execute your command. That is almost the same as using npm
FROM node:12-slim AS build
WORKDIR /usr/src/app
COPY package.json package-lock.json ./
RUN npm ci --production && npm clean cache --force
# don’t do that, it will start bash
CMD "node server.js"Starting with npm, here’s the process tree:
$ ps falx
UID PID PPID COMMAND
0 1 0 npm
0 16 1 sh -c node server.js
0 17 16 \_ node server.js
There is no advantage to those two extra processes.
Sources:
https://maximorlov.com/process-signals-inside-docker-containers/
https://github.com/nodejs/docker-node/blob/master/docs/BestPractices.md#handling-kernel-signals