Docker compose up 'Exec format error' loading a library

Question

I'm developing a multi-module docker nodejs app with docker-compose. There's an issue with the natural node package needed by a module. It seems that it can't exec it. I tried to rebuild it on the fly with a RUN command, but nothing changed. Here's the log when trying to run docker-compose up:

web_1         | /app/web-server/node_modules/natural/lib/natural/classifiers/classifier.js:32
web_1         |     if (e.code !== 'MODULE_NOT_FOUND') throw e;
web_1         |                                        ^
web_1         |
web_1         | Error: Error loading shared library /app/web-server/node_modules/webworker-threads/build/Release/WebWorkerThreads.node: Exec format error
web_1         |     at Error (native)
web_1         |     at Object.Module._extensions..node (module.js:597:18)
web_1         |     at Module.load (module.js:487:32)
web_1         |     at tryModuleLoad (module.js:446:12)
web_1         |     at Function.Module._load (module.js:438:3)
web_1         |     at Module.require (module.js:497:17)
web_1         |     at require (internal/module.js:20:19)
web_1         |     at bindings (/app/web-server/node_modules/bindings/bindings.js:81:44)
web_1         |     at Object.<anonymous> (/app/web-server/node_modules/webworker-threads/index.js:1:105)
web_1         |     at Module._compile (module.js:570:32)
web_1         |     at Object.Module._extensions..js (module.js:579:10)
web_1         |     at Module.load (module.js:487:32)
web_1         |     at tryModuleLoad (module.js:446:12)
web_1         |     at Function.Module._load (module.js:438:3)
web_1         |     at Module.require (module.js:497:17)
web_1         |     at require (internal/module.js:20:19)

Here's the package.json:

{
  "name": "realaffinities",
  "version": "1.0.0",
  "description": "",
  "main": "server/Server.js",
  "keywords": [],
  "author": "",
  "license": "GPL-3.0",
  "dependencies": {
    "async": "^2.5.0",
    "big-integer": "^1.6.23",
    "body-parser": "1.9.0",
    "express": "^4.15.3",
    "express-validator": "^3.2.1",
    "knex": "^0.13.0",
    "mysql": "^2.14.1",
    "natural": "^0.5.4",
    "twit": "^2.2.9",
    "url-exists": "^1.0.3",
    "nodemon": "^1.11.0"
  },
  "devDependencies": {
    "grunt": "^1.0.1",
    "grunt-express-server": "^0.5.3",
    "mocha": "^3.4.2",
    "supertest": "^3.0.0",
    "bcrypt": "1.0.2"
  },
  "scripts": {
    "test": "mocha web-server/test",
    "start": "node server/Server.js"
  }
}

My dockerfile:

FROM node:6.11-alpine

EXPOSE 3000
ENV NODE_ENV development
RUN mkdir /app
WORKDIR /app

# add package.json and run npm install before adding the rest of the files
# this way, you only run npm install when package.json changes
ADD /web-server/package.json /app/package.json

RUN apk add --no-cache make gcc g++ python

RUN npm install -g mocha
RUN npm install

I don't know whether it's an issue of this particular node package or a knowledge lack of mine. If I run the same application locally on my mac without docker, it doesn't encounter this problem.

Solution

Someone reported same problem in this issue and his case was similar to yours. As discussed in comments, this worked for you, so I am posting this as answer also:

It sounds like it's trying to load a native extension that wasn't compiled for linux (in the container) -- maybe you previously installed the extension on OS X and it's trying to load that binary. If you mean this is a node app, try just removing node_modules and run npm install again

Fix that worked for you: rm -rf node_modules