Monitoring clusters

When we are designing a software system, we undertake many explicit and implicit assumptions. We always try to make the best decisions based on our knowledge, but there may be some parameters that we have underestimated or didn’t take into account.

Using monitoring, we can validate our assumptions and verify that our application performs as intended and scales as expected. Good monitoring systems are also vital for detecting software bugs and helping us detect early potential security incidents.

The following screenshot shows the wealth of options for monitoring in MongoDB Atlas. Detailing each and every metric is outside the scope of this chapter, but it’s important to have at least a cursory understanding of what each metric measures.

Figure 9.1 – MongoDB Atlas monitoring metrics

What should we monitor?

By far the most important metric to monitor in MongoDB is memory usage. MongoDB (and every database system...