nodebestpractices/sections/docker/bootstrap-using-node.md

Bootstrap container using node command instead of npm

One paragraph explainer

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 #716). 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'].

Code example

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']

Antipatterns

Using npm start

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!
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 process.

Sources:

https://maximorlov.com/process-signals-inside-docker-containers/

https://github.com/nodejs/docker-node/blob/master/docs/BestPractices.md#handling-kernel-signals