Ctop will help you see what's going on at the container level. Basically, containers are a logical group of processes isolated using kernel's cgroups and namespaces. Recently, they have been made popular by Docker and they are also heavily used under the hood by systemd and a load of container tools like lxc, rocket, lmctfy and many others.

Under the hood, ctop will collect all metrics it can from cgroups in realtime and render them to instantly give you an overview of the global system health.

It currently collects metrics related to cpu, memory and block IO usage as well as metadata such as owning user (mostly for systemd based containers), uptime and attempts to guess the container managing technology behind.