PM2 - Tools

This package contains a few tools to monitor and use PM2 behind a load balancer like ELB in AWS.

REST - Interface

Will start a server on the specified port with currently the following endpoints

• /healthcheck => returns 200 if at least one of the watched processes is still live
• /metrics => wraps the pm2 list command and returns the following structure

{
    "processes": [{
        "process": {
            "memory": "<usage in bytes>",
            "cpu": "<cpu usage in %>"
        },
        "restarts": "<number of restarts>",
        "status": "<current process status (online...)>",
        "name": "<name of the app>"
    }],
    "metrics": {
        "<name>": "<metric data>"
    }
}

Usage

Let your application run with PM2, either via JSON or directly via command line and additionally run this script.

'use strict';

const RestService = require('pm2-tools').RestService;

const app = new RestService({
    monitor_apps: ['my-application'] // if you just want to monitor specific apps
});

app.connect().then(function () {
    app.listen(7979)
});

The passed options monitor_apps allows you to control which PM2 applications you want to monitor. If not passed all will be monitored.

Via PM2

Another possibility is to also start the status/metric server with PM2.

{
  "apps": [
    {
      "name": "status",
      "script": "src/status.js",
      "instances": 1,
      "max_memory_restart": "200M"
    },
    {
      "name": "my-app",
      "script": "src/server.js",
      "instances": 4,
      "max_memory_restart": "200M",
      "exec_mode": "cluster"
    }
  ],
}

The only important config is the the above described monitor_apps which needs to be set to ['my-app'] to deliver the correct status, else we would take status into account too and would never get a bad healthcheck.

For Docker finally start with pm2 --no-daemon pm2.json to keep Docker alive or without --no-daemon for any other environment.

Metrics

There are 4 different built in metrics.

• Counter => a simple counter which requires no params
• MultiCounter => like counter but accepts one additional param to count for examples requests paths
• Average => a simple average counter to measure response times
• MultiAverage => like average it accepts an additional param that allows to measure for example different averages of request paths

Usage

Register

Before using a custom metric it needs to be registered.

    var MultiAverage = require('pm2-tools').Metrics.MultiAverage;

    instance.registerMetric('request_time_by_path', new MultiAverage());

Sending data to metrics

The application it self can use the MessageBus to publish metrics.

var MessageBus = require('pm2-tools').MessageBus;
var bus = new MessageBus();

bus.publish('request_time_by_path', new Date() - start, '/my-url');