Zero downtime deploys with PM2

[eldoy]

Using PM2 we can have zero downtime deploys. Start pm2 with systemd, then let pm2 handle the apps.

Here is setup with NGINX:

https://pm2.keymetrics.io/docs/tutorials/pm2-nginx-production-setup

Here is how to setup app:

https://pm2.keymetrics.io/docs/usage/signals-clean-restart/