kubernetes: enforce resource limits using LimitRange

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If we want to make sure the resources for a given namespace are controlled yet we want to be able to give full control to whoever is creating objects in that namespace, we can use LimitRange to enforce some resource constraints:

• We can enforce a minimum and maximum (and it's default value) for compute resources per Pod or Container or storage request per PersistentVolumeClaim in the namespace
• We can also enfornce a ratio between request and limit for a resource (so that we are not abusing the control setting limits that are too wide) Set default request/limit for compute resources in a namespace and automatically inject them to Containers at runtime.

This is implemented as an admission controller that observes the incoming requests and makes sure that it does not violate any of the constraints enumerated in the LimitRange object within it's namespace.

02/06/2021