As discussed in part 1 of this series, Docker can rightly be classified as a type of mini-host. Just like a regular host, it runs work on behalf of resident software, and that work uses CPU, memory, I/O, and network resources. However, Docker containers run inside cgroups which don't report the exact same metrics you might expect from a host. This article will discuss the resource metrics that are available. The next article in this series covers three different ways to collect Docker metrics.