Voxer released a Node metrics library called Zag (https://github.com/Voxer/zag) to aggregate and visualize metrics in real time. The library contains multiple components (server and agent) and supports two backend storages at the moment: LevelDB and Postgres (recommended for production use). We will have to host this application on our own servers.

During this chapter, we tackled different metrics that can be collected and monitored by writing custom code for our applications. However, it's good to know that there are several (commercial) applications that gather a lot of data about our application (including information that we have not talked about, such as garbage collection), such as Nodetime, StrongOps, or Concurix.

A topic that we have not covered in depth in this chapter is uptime monitoring. An Express application might be unavailable at some point in time because of various reasons (such as network outage or an instance temporarily down for maintenance...