Keep a node application constanly running:
*Use PM2 as a process manager
PM2 lets you run your nodejs scripts forever. In the event that your application crashes, PM2 will also restart it for you.
Install PM2 globally to manager your nodejs instances
npm install pm2 -g
Navigate to the directory in which your nodejs script resides and run the following command each time you want to start a nodejs instance to be monitored by pm2:
pm2 start server.js --name "app1"
pm2 list
pm2 stop <instance named>
pm2 delete <instance name>
pm2 restart <instance name>
pm2 monit
pm2 kill
pm2 reload <instance name>
pm2 logs <instance_name>