Why bcrypt (Node.js) package causes "Docker Failed - bcrypt_lib.node: Exec format error" while many other packages are not in the same conditions?

I have checked the issue Error while building a docker image in the node.bcrypt.js repository and the Stack Overflow topic Docker Failed - bcrypt_lib.node: Exec format error. Altgough some solutions has been suggested there, none of them has satisfied me, and also it is still unclear WHY bcrypt packages causes this error.

Please do not copy node_modules inside Docker. It decreases your build time and prevents this kind of errors from happening.

https://github.com/kelektiv/node.bcrypt.js/issues/824#issuecomment-677485592

does not answer this question because all other packages I installed works fine (I'll list them in the appendix). And, it is not the solution - it running away from the problem because it is something wrong with the bcrypt package.

That is why I have started my own investigation and myfirst question is WHY bcrypt package requies the special attention to itself? What exacly wrong with it? Why it as the bad comatibility with the Docker?

docker.compose.yaml

Unlike the Docker Failed - bcrypt_lib.node: Exec format error topic, I have no Dockerfile (for the local development mode). Also, need to start the Nodemon from the FrontServer service.

version: "3.5"

services:

  FrontServer:

    image: node:18-alpine
    container_name: Example-Local-FrontServer
    ports: [ "8080:8080" ]

    # [ Theory ] Nodemon will not be found if invoke just "nodemon". See https://linuxpip.org/nodemon-not-found/
    # [ Theory ] About -L flag: https://github.com/remy/nodemon/issues/1802
    command: sh -c "cd var/www/example.com && node_modules/.bin/nodemon -L 03-LocalDevelopmentBuild/FrontServerEntryPoint.js --environment local"

    depends_on: [ Database ]

    volumes:
      - type: bind
        source: .
        target: /var/www/example.com

  Database:

    image: postgres
    container_name: Example-Local-Database
    ports: [ "${DATABASE_PORT}:${DATABASE_PORT}" ]

    environment:

      - "POSTGRES_PASSWORD=${DATABASE_PASSWORD}"

    volumes:
      - DatabaseData:/var/lib/postgresql/data

volumes:
  DatabaseData:
    name: Example-Local-DatabaseData
    driver: local

Other Node.js dependencies

Unlike the bcrypt, below dependencies does not cause the Exec format error:

{
  "private": "true",
  "dependencies": {
    "@yamato-daiwa/es-extensions": "1.7.0-alpha.4",
    "@yamato-daiwa/es-extensions-nodejs": "1.7.0-alpha.4",
    "body-parser": "1.20.2",
    "class-transformer": "0.5.1",
    "class-validator": "0.14.0",
    "cors": "2.8.5",
    "express": "4.18.2",
    "express-handlebars": "7.1.2",
    "jsonwebtoken": "9.0.2",
    "morgan": "1.10.0",
    "multer": "1.4.5-lts.1",
    "passport": "0.6.0",
    "passport-jwt": "4.0.1",
    "pg": "8.11.3",
    "qs": "6.11.2",
    "reflect-metadata": "0.1.13",
    "routing-controllers": "0.10.4",
    "typeorm": "0.3.17"
  }
}

Solution

Generally the issue is that you downloaded bcrypt for a specific CPU architecture, but you're running your container on a different architecture.

Examples of CPU architectures are arm, amd64, powerpc, riscv.

This specifically happens with packages like bcrypt, is because they ship with a compiled binary where most packages are pure Javascript. When you run npm install, it will find the appropriate pre-compiled binary for you that runs on your specific CPU. If you copy that into the docker container and run the docker container on a different arch you get this error.

If this is happening on your local machine, then my best guess is that you're on a Mac (ARM architecture), and Docker is running in Rosetta (amd64), but there's other setups that yield these kinds of results.