My troubles getting to run a Node application with PM2 in cluster mode with NVM

By Adrian Matei

In this blog post I will list of the troubles I went through getting to run the API on
PM21 in cluster mode on an Ubuntu system with Node.js managed by NVM. The PM2 setup was on a single node (aka fork mode)
until now with no problems, but I decided to take advantage of the multi-core capability and enable cluster mode with PM2.


Configure PM2 in cluster mode as advised in the documentation1. Make sure you use the Node.js version you want PM2 to run on
and update PM2 to the latest version2 (Thus you find out you need to remove interpreter from the configuration). Disable the old version
of installed pm2 service in systemd (systemctl disable pm2.service) and enable the new one (e.g. systemctl enable pm2-ama.service).
Reboot your system.

To run the API on different versions of Node.js easily I use nvm. Solving this nvm issue3,
resulted in an elegant solution how you can do that .
I am using a .json file to start the pm2 process and below is the working configuration in single mode (fork mode):

   apps : [{
     name : '',
     script : 'bin/www',
     interpreter : "node@10.15.0",
     env: {
       "NODE_ENV": "development",
       "YOUTUBE_API_KEY" : "AIxxx..."
     env_production : {
        "NODE_ENV": "production",
        "YOUTUBE_API_KEY" : "AIxxx...",
        "OTHER_ENV_VARIABLES" : "some-values"

Running in cluster mode

According to the documentation2 it should be fairly easy.
I would just start the application with the following new parameters:

    instances : "max",
    exec_mode : "cluster"

So I though the .json config file should look something like the following:

  apps : [{
    name : '',
    script : 'bin/www',
    interpreter : "node@10.15.0",
    instances : "max",
    exec_mode : "cluster",
    env: {
      "NODE_ENV": "development",
      "YOUTUBE_API_KEY" : "AIzaSyCCo1VvwO8iMfxgquoYzyYM-A5eeyvJR4Q"
    env_production : {
       "NODE_ENV": "production",
       "YOUTUBE_API_KEY" : "AIxxx...",
       "OTHER_ENV_VARIABLES" : "xxxxx"

It did not work, the cluster started instances errored with the following message:

usersRouter.get('/:userId', keycloak.protect(), async (request, response) => {
SyntaxError: Unexpected token (
    at Object.exports.runInThisContext (vm.js:78:16)
    at Module._compile (module.js:543:28)

Looking more exactly with pm2 monit, I saw the instances started with the wrong Node version (7.4.0) when
I was actually expecting 10.15.0:

App Name                                                                                                           │
Namespace             undefined                                                                                                                                    │
Version               undefined                                                                                                                                    │
Restarts              82                                                                                                                                           │
Uptime                0s                                                                                                                                           │
Script path           /home/ama/projects/                                                                                             │
Script args           N/A                                                                                                                                          │
Interpreter           node@v10.15.0                                                                                                                                │
Interpreter args      N/A                                                                                                                                          │
Exec mode             cluster                                                                                                                                      │
Node.js version       7.4.0

That explains the error above, because async-await was not supported until version 8 of Node.

So next is to find out is why it was starting with an old version. This was not even a version managed
by nvm (nvm list).

Unlink old node executable in /usr/local/bin

The old version (7.4.0) is from an initial installation of Node.js I used before switching to NVM. It was even
configured in /usr/local/bin:

whereis node
node: /usr/local/bin/node /opt/node/bin/node

This might be it – change this symlink to the newer Node.js version.

Update to the latest LTS Node.js version with NVM (optional)

It was time to update to the newest LTS version. Find the latest LTS version:

nvm ls-remote --lts | grep -i latest

v4.9.1   (Latest LTS: Argon)
v6.17.1   (Latest LTS: Boron)
v8.17.0   (Latest LTS: Carbon)
v10.22.0   (Latest LTS: Dubnium)
v12.18.3   (Latest LTS: Erbium)

Then install the version v12 with the following command nvm install v12.18.3

Verify the version is installed, use it and set it as default :

$ nvm list
->       v10.15.0

nvm use 12
nvm alias default 12

Now I could update the /usr/local/bin symlink.

unlink /usr/local/bin/node
ln -s /home/ama/.nvm/versions/node/v12.18.3/bin/node /usr/local/bin/node

Reboot, but it still doesn’t work – it means pm2 does not use the new Node as configured.

First – update PM2

The pm2 version I was using was 2.7.0, and I thought it might be time for an update. This is very easy done by following the instructions4
in the documentation:

pm2 save #save all your processes
npm install pm2 -g #then install the latest PM2 version from NPM
pm2 update #finally update the in-memory PM2 process

Update the startup script because I have upgraded the Node.js version

pm2 unstartup
pm2 startup

This generates the following startup script:

[PM2] Init System found: systemd
[PM2] To setup the Startup Script, copy/paste the following command:
sudo env PATH=$PATH:/home/ama/.nvm/versions/node/v12.18.3/bin /home/ama/.nvm/versions/node/v12.18.3/lib/node_modules/pm2/bin/pm2 startup systemd -u ama --hp /home/ama

You need to execute the sudo env ... command.

That did not do it either, the app was still starting with the old Node.js version. The advantage now wasthe error message clearly indicated
that I cannot specify an interpreter when starting the app in cluster mode.
“Yes in fork mode you can defined the interpreter but in cluster mode it’s not possible
as we rely on the current Node.js version that runs PM2 to use the cluster module

Another strange thing noticed when running the pm2 status was it was complaining
that in memory I was still using the older version and need to execute pm2 update to use the new. But
when I ran pm2 --version in the terminal it would display the latest one.

Reboot did not help either

Investigate startup services

Thinking about possible causes led me to investigate the startup services I configured long time ago with systemd.

I got lucky with the following command:

systemctl list-units --type=service | grep -i pm2
pm2.service                    loaded active running PM2 process manager

Having now a closer look at it:

systemctl cat pm2.service

Description=PM2 process manager


ExecStart=/usr/local/lib/node_modules/pm2/bin/pm2 resurrect --no-daemon
ExecReload=/usr/local/lib/node_modules/pm2/bin/pm2 reload all
ExecStop=/usr/local/lib/node_modules/pm2/bin/pm2 kill


I see the “old” node version is still in place, both in the Environment config Environment=PATH=/opt/node/bin:/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin and
in the entries ExecStart,ExecReload and ExecStop.

But, what about the new PM2 that I installed in the newer Node.js version? Well, it seems to be inactive and
it can be found under the name pm2-ama.service.

systemctl status pm2-ama.service

● pm2-ama.service - PM2 process manager
   Loaded: loaded (/etc/systemd/system/pm2.service; disabled; vendor preset: enabled)
   Active: inactive (dead)

The solution that proved successful was to enable the new service and deactivate the other:

sudo systemctl disable pm2.service
sudo systemctl enable pm2-ama.service
sudo reboot

Verify and confirm everything looks good now:

$ systemctl cat pm2-ama.service
# /etc/systemd/system/pm2-ama.service
Description=PM2 process manager


ExecStart=/home/ama/.nvm/versions/node/v12.18.3/lib/node_modules/pm2/bin/pm2 resurrect
ExecReload=/home/ama/.nvm/versions/node/v12.18.3/lib/node_modules/pm2/bin/pm2 reload all
ExecStop=/home/ama/.nvm/versions/node/v12.18.3/lib/node_modules/pm2/bin/pm2 kill


This fixed the problem, and the application runs now with pm2 in cluster mode.

It’s been a while since I did this kind of “operations” investigation, but this can be as fun.


My troubles getting to run a Node application with PM2 in cluster mode with NVM was originally published by CodepediaOrg at CodepediaOrg on September 08, 2020.