I've been running a reasonably large kubernetes cluster (~600 cores) in production for the last 6 months or so. I've had to deal with hotspots, both IO, CPU and load (which could be either). Getting requests and limits dialed has been a bit of a challenge.

I worked with Mesos a bit last year and miss the sophistication of the scheduler. Granted, I never ran it at the same scale, but I felt like the approach was much easier to grok.

I've seen a few projects floating around meant help dynamically tune resource utilization in k8s. By this time next year, I imagine those will be fairly commonplace. I'm definitely looking forward to using descheduler:

https://github.com/kubernetes-incubator/descheduler