The current craze of Docker has everyone sticking their processes inside a container… but do you really understand cgroups and how they work? Do you understand the difference between CPU Sets and CPU Shares? Spark is a Scala application that lives inside a Java Runtime, do you understand the consequence of what impact the cgroup constraints have on the JRE? This talk starts with a deep understand of Java’s memory management and GC characteristics and how JRE characteristics change based on core count. We will continue the talk looking at containers and how resource isolation works. The session will detail specifically the difference between CPU sets and CPU shares and memory management. The session will close with a deep understanding of the consequences of running the JRE in a CPU share environment and the potential for pseudo-random behavior of running in a heterogeneous datacenter.