We are running our Node.js process inside an ephemeral SSH session. When we log out, the host machine will kill any processes initiated during that session. Therefore, we need to come up with a way of keeping our process alive even after logging out.
Furthermore, no matter how good our code base is, or how complete our test plans are, in any application of significant size, there will be errors. Sometimes, these errors are fatal and crash the application. In these instances, we should log the error and notify the developers, but most importantly, we should restart the application as soon as it crashes.
Ubuntu provides the upstart daemon (upstart.ubuntu.com), which can monitor a service and respawn it if it dies unexpectedly. Likewise, there's a popular npm package called forever (github.com/foreverjs/forever), which does a similar job. However, I have found PM2 (pm2.keymetrics.io) to be the best process manager out there, so that's what we'll use in this book...
