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Node.js Tooling I – Processmanager PM2

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The purpose of this post is to help you get started with tools for Node.js in general and Loopback specifically to ease you life as Developer and Operator.


You need a Node.js based API (to follow through this article. PM2 supports other languages too).

PM2 Processmanager

The PM2 Processmanager is a mighty one with many different options, has various integrations and even supports an online monitoring.

In this Article I present you the basic usage of it to get started fast. In a later Article I will help you migrate to Docker and add the online monitoring of your processes.


The Installation is as easy as npm install pm2 -g. It is important that you install it globally.

How to use it

You can manually start an api by issuing pm2 start app.js, but then you have to specify all parameter on every start. So it could be fast to test, but I recommend writing a small configuration file for it name process.yml.

Configuration Syntax

PM2 offers multiple syntax variants for the configuration file. Currently they support Javascript, JSON and YAML format. I prefer to create this configuration in YAML so I will present it to you in this syntax. For the others please have a look at Process Configuration File Syntax (1)


Most often my configuration looks like this:

  - script: path_to_startup_script
    name: api_name
    exec_mode: cluster
    instances: 1
      DEBUG_FD: 1

apps is the root element.

Each script entry refers to an app or api that should be started. Here you define the path to the file that starts your api.

You can either define one app per app/api or you can even define a stack you want to start with multiple entries.

Personally I use one configuration file per api in development and one configuration for a stack in the staging environment before I deploy to docker.

The name describe the name you will see in the process manager when you list the running processes.

With exec_mode and the following instances things get interesting. If you define the mode fork you can only start up one instance of this app/api. But if you define cluster then you´re able to scale the app/api with one single command and pm2 will load balance it for you!

instances defines how many concurrent instances you want to launch of this app/api at startup. I set this normally to 1 and adjust on the fly according to the needs.
This way I can already get a first idea of the need to scale.

With the env you can specify environment variables you want to set.
DEBUG_FD: 1 tells Node.js to change the output stream to process.stdout.
DEBUG_COLORS: 1 will add colors to the pm2 log output. This is handy because you see on the first glance if the logs message is an error or not.

These have not been all possibly Attributes for the configuration file. If you want a tighter control have a look at the Configuration File Attributes (2).

After this explanation you will find my configurations for a Express based API and a Loopback based API.

Express Example

  - script: bin/www
    name: api
    exec_mode: cluster
    instances: 1
      DEBUG_FD: 1
      NODE_ENV: staging

Loopback Example

  - script: server/server.js
    name: loopback_api
    exec_mode: cluster
    instances: 1
      DEBUG_FD: 1


After we defined the configuration we need to interact with the Processmanager to start and stop our APIs and check the log output.

Listing currently running Processes

To view all currently running Processes issue pm2 list at a console.

Start an API with an process.x

Starting your API with an configuration file is as easy as the command pm2 start process.x (x is config.js, json or yml).
After this command PM2 starts your API with the specified configuration and outputs it list of currently running processes.

Stopping an API

You can stop your API with pm2 stop process.x.
Important to know is that PM2 just stops your API then, but won´t remove it from the prepared to run process list. If you want to remove it cleanly and make sure on the next start you have a clean plate you have to destroy it.

Destroying an prepared to run API entry

To remove a API entry from the prepared to run list you issue pm2 delete process.x

Check the Logs

To check all logs without filtering to one API you issue pm2 logs.

If you want to filter the logs to one specific API you can add it to the command like this pm2 logs name_of_your_api

If you have any question post them into the comments. Or feel free to send my an email.

Yours sincerely,