As an OpenStack cluster is scaled out, the number of moving parts that can get jammed increases. As you have seen, each server added to the cluster will run more than one service. Each of those services interacts and communicates with each other across the cluster, using different communication methods and unique endpoints for each service. This presents a complicated web of interdependence that can be very complicated to debug when something goes wrong. Monitoring all the moving parts can save a large amount of time and hassle in trying to figure out what has gone wrong when things stop working.
In this chapter, we will look at setting up monitoring for the cluster to help you have a detailed view of the general health of a running OpenStack cluster.
There are two classifications of monitoring, performance monitoring and availability monitoring. Performance monitoring shows the performance of what is being monitored over time. Availability monitoring show the status of what is being monitored at a point in time. Often, the same things are monitored, but the purposes of the two types of monitoring are different. As an example, if a server's CPU utilization was being monitored, availability monitoring checks the CPU utilization, and if it breaches a certain threshold, the monitoring alerts an operator that the utilization is high or may have remained high over the most recent checks. Performance monitoring keeps track of the CPU utilization in the longer term and most likely creates a graph to show the trend of CPU utilization on a server across days or weeks or longer.
In this chapter, we will focus on availability monitoring to be able to determine the current health of an OpenStack cluster based on the current status of the checks being run on the servers in the cluster.