The go-demo (https://github.com/vfarcic/go-demo) service is already instrumented with a few metrics. However, they do not mean much by themselves. Their usage starts only once Prometheus scrapes them. Even then, they provide only a visual representation and the ability to query them after we find a problem. The major role of graphs and the capacity to query metrics comes after we detect an issue and we want to drill deeper into it. But, before we get there, we need to set up alerts that will notify us that there is a problem.
We cannot think about metrics before we have some data those metrics will evaluate. So, we'll start from the beginning and explore how to let Prometheus know that metrics are coming from services we instrumented. That should be a relatively easy thing to accomplish since we already have all the tools and processes...