Simple docker monitor in node.js

docker-monitor.js

// simple script to monitor a docker engine
// 14 March 2016
// https://docs.docker.com/engine/reference/api/docker_remote_api_v1.22/#monitor-docker-s-events
const https = require('https');
const fs = require('fs');

// for now we use a dummy registry, but we could link this to consul, etcd etc..
var registry={};

// setup TLS config to be able to talk to docker, when run in a container we
// could use the unix socket as well avoiding the need for TLS
const certdir = process.env.HOME + '/.docker/machine/certs/';
const URL = process.env.DOCKER_HOST;
const hostparams = URL.match(/tcp:\/\/(.+):(\d+)/);

const options = {
  hostname: hostparams[1],
  port: hostparams[2],
  method: 'GET',
  key: fs.readFileSync(certdir + 'key.pem'),
  cert: fs.readFileSync(certdir + 'cert.pem'),
  ca: fs.readFileSync(certdir + 'ca.pem')
};

// how to pickup events, we are only interested in container events of type "start" and "die"
// clone the options and add specific items
const eventsOptions = Object.assign({},options, {
  path: '/events?filters={"event":{"start":true,"die":true},"type":{"container":true}}',
  agent: false
});

// clone the options to use them for docker inspect
const inspectOptions = Object.assign({},options);

// start picking up events
const req = https.request(eventsOptions, (res) => {
  //console.log('statusCode: ', res.statusCode);
  //console.log('headers: ', res.headers);

  res.on('data', (d) => {
	const data=JSON.parse(d.toString());
	if (data.status == "start"){
		handleStart(data.id);
	}
	if (data.status == "die"){
    // remove the item from the registry
		registry[data.id] = undefined;
    // and show the registry
		console.log("Registry:",JSON.stringify(registry));
	}
  });
});
req.end();

// we are interested in SERVICE_* items passed to the enviroment at startup
function filterEnv(envData){
	var envObj={};
	envData.forEach((item) => {
		if (item.match(/^SERVICE_/)){
			var arr = item.split("=",2);
			envObj[arr[0]] = arr[1];
		}
	});
	return envObj;
}

// change "80/TCP" into 80
function normalizePort(portData){
   return Number(portData.split("/")[0]);
}

// when a start event is detected, inspect the container to find the data we need
function handleStart(id){
	inspectOptions.path = `/containers/${id}/json`;
	const iReq = https.request(inspectOptions,(res) => {
		 res.on('data', (d) => {
			const data=JSON.parse(d.toString());
      const envData = filterEnv(data.Config.Env);
			const item = {
				"ID": data.Config.Hostname,
        "Name": envData.SERVICE_NAME,
        "Tags": [ envData.SERVICE_TAGS],
				"Port": normalizePort(Object.keys(data.Config.ExposedPorts)[0]),
				"Address": data.NetworkSettings.Networks.bridge.IPAddress
			}
      // add the results to the registry
			registry[id] = item;
      // and show the registry
			console.log("Registry:",JSON.stringify(registry));
		});
	});
	iReq.end();
	iReq.on('error', (e) => {
		console.error(e);
	});
}


req.on('error', (e) => {
  console.error(e);
});