Running a Node.js app with PM2 and Nginx

# Node.js LTS from NodeSource
curl -fsSL https://deb.nodesource.com/setup_lts.x | bash -
apt install -y nodejs
npm install -g pm2

# start your app (from its folder)
pm2 start npm --name myapp -- start
pm2 save
pm2 startup            # follow the command it prints

Serve it on your domain with Nginx

In /etc/nginx/sites-available/example.com:

server {
    server_name example.com www.example.com;
    location / {
        proxy_pass http://127.0.0.1:3000;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Enable it, reload Nginx, then add HTTPS with Certbot.