Just a quick one, since I recently found out about Pixie which is a super interesting opensource project recently bought by NewRelic.
It's an agent which you can install on your k8s cluster (or on your standard VM). It uses eBPF to collect deep data from Linux Kernel, granting the ability to monitor an application without the need of an APM (Application Performance Management). It promises a maximum 5% overhead.
The frontend uses PxL Script (which is similar to python + panda) to fetch data from backend, which is queried directly.
That's a great video from Pixie explaining the technology in details: https://www.youtube.com/watch?v=shJ45UJvFR4.