Why is my NodeJS process hanging in Docker?

README.md

Establish the directory structure

• README.md
  • docker-compose.yml
  • worker/package.json
  • worker/src/utils.js
  • worker/src/sampleNodeProcess.js

Run the experiment

• Terminal A:

  1. Install dependencies: docker-compose run worker npm install
  2. Run the sample nodejs process: docker-compose run worker node src/sampleNodeProcess

• Terminal B:

  1. Find the name of the docker container which is runnign the process:

  $ docker ps -a
  CONTAINER ID   IMAGE   COMMAND                 CREATED        STATUS        PORTS  NAMES
  90ed79aa7ac5   node:7  "node src/sampleNo..."  8 seconds ago  Up 6 seconds         worker_run_12
  

  1. Send an interrupt to the appropriate container name: docker stop worker_run_12

• Terminal A

  1. You should see that the process exited gracefully:

  trapSignals ... server started
  {"name":"sp-json-logger","hostname":"...","pid":1,"level":40,"application":"","program":"","language":"","log":{"message":"server stopped by SIGTERM"},"msg":"","time":"...","v":0}
  [WTF Node?] open handles:
  - File descriptors: (note: stdio always exists)
    - fd 1 (tty) (stdio)
    - fd 2 (tty) (stdio)
  - Servers:
    - <unknown address>
      - Listeners:
        - request: (anonymous) @ /apps/src/lib/trapSignals.js:8
  

docker-compose.yml

version: '3.1'

services:

  worker:
    #restart: always
    image: node:7
    env_file:
        - ./worker/.env
    volumes:
      - ./worker/src:/apps/src
      - ./worker/node_modules:/apps/node_modules
      - ./worker/package.json:/apps/package.json
    working_dir: /apps

package.json

{
  "license": "ISC",
  "dependencies": {
    "sp-json-logger": "1.0.9"
  },
  "devDependencies": {
    "wtfnode": "0.5.4"
  }
}

sampleNodeProcess.js

'use strict';

const wtfnode = require('wtfnode');
const logger = require('sp-json-logger');

var http = require('http');

var server = http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n');
}).listen(3000, '0.0.0.0');

console.log('trapSignals ... server started');

const utils = require('../lib/utils');

var shutdown = function shutdown(signal, value) {
  server.close(function () {
    logger.warn( { log: { message: 'server stopped by ' + signal } } );
    wtfnode.dump();
    process.exit(128 + value);
  });
};

utils.registerForGracefulShutdown(shutdown);

utils.js

/**
 * Idea came from https://medium.com/@gchudnov/trapping-signals-in-docker-containers-7a57fdda7d86
 * 
 * @param {*} shutdown - the calling code user this method to control what actions to take as part of shutdown
 */
var registerForGracefulShutdown = function registerForGracefulShutdown(shutdown) {
  var signals = {
    'SIGINT': 2,
    'SIGTERM': 15
  };

  Object.keys(signals).forEach(function (signal) {
    process.on(signal, function () {
      shutdown(signal, signals[signal]);
    });
  });
};

module.exports = {
  registerForGracefulShutdown: registerForGracefulShutdown
};