Optimizing Dockerfile for smaller image size - node.js

Question

I'm trying to build a docker image which is as small as possible. My project is codded in typescript.
For what I have at the moment, it works just fine, but I'm sure not if my implementation is even good. When I run docker build the image size comes up to 276.23MB.
The problem is that I have to call "tsc" to compile my code into JavaScript which is a dev-dependency.
This is my Dockerfile:
FROM node:16-alpine3.11 as build
WORKDIR /usr/src/app
COPY . /usr/src/app/
RUN \
npm install && \
npm run build
FROM node:16-alpine3.11
WORKDIR /app
COPY --from=build /usr/src/app .
CMD [ "npm", "start" ]
These are the scripts & dependencies in my package.json file:
{
...
"scripts": {
"test": "jest --coverage",
"test:watch": "jest --watch",
"start": "fastify start -l info dist/src/app.js",
"build": "npx rimraf /dist && tsc",
"prebuild": "ts-node scripts/clean",
"docker": "docker build -t barnes-biz/pokemon:1.0.0 .",
"predocker": "npm run build",
},
"dependencies": {
"fastify": "^3.0.0",
"fastify-autoload": "^3.3.1",
"fastify-cli": "^2.13.0",
"fastify-helmet": "^5.3.2",
"fastify-plugin": "^3.0.0",
"fastify-sensible": "^3.1.0",
"fastify-swagger": "^4.8.3",
"mongoose": "^5.13.5",
"weak-napi": "^2.0.2"
},
"devDependencies": {
"#types/jest": "^26.0.23",
"#types/node": "^15.0.0",
"#types/rimraf": "^3.0.1",
"#typescript-eslint/eslint-plugin": "^4.28.0",
"#typescript-eslint/parser": "^4.28.0",
"concurrently": "^6.0.0",
"cross-env": "^7.0.3",
"eslint": "^7.29.0",
"eslint-config-prettier": "^8.3.0",
"eslint-plugin-prettier": "^3.4.0",
"fastify-tsconfig": "^1.0.1",
"jest": "^27.0.5",
"prettier": "^2.3.2",
"rimraf": "^3.0.2",
"ts-jest": "^27.0.3",
"ts-node": "^10.0.0",
"typescript": "^4.2.4"
}
}
I don't seem to understand how to do it. Can you help me? Do you also know some best practices that I should follow writing the Dockerfile or anything else? Thank you!

Answer 1

A couple of things:
You want to copy the output of the compiler, not the source files
You still need to install node_modules in the running container, but want to use the production flag to make sure dev dependencies are ignore. The docker file will then look something like this:
FROM node:16-alpine3.11 as build
WORKDIR /usr/src/app
COPY package*.json ./ # A small optimization to allow for caching in between Docker builds
RUN npm ci
COPY . /usr/src/app/
RUN npm run build
FROM node:16-alpine3.11
WORKDIR /app
COPY package*.json ./
RUN npm ci --production
COPY --from=build /usr/build/app . # This line will depend on your tsconfig
RUN ls -la
CMD [ "npm", "start" ]
You could alternatively prune your node_modules in the build image and copy that over as well.