Kubernetes originally only supported Docker as a container runtime engine. But that is no longer the case. Kubernetes now supports several different runtimes:
- Docker (through a CRI shim)
- Rkt (direct integration to be replaced with rktlet)
- Frakti (Kubernetes on the hypervisor, previously Hypernetes)
- Rktlet (CRI implementation for rkt)
A major design policy is that Kubernetes itself should be completely decoupled from specific runtimes. The Container Runtime Interface (CRI) enables this.
In this section, you'll get a closer look at the CRI and get to know the individual runtime engines. At the end of this section, you'll be able to make a well-informed decision about which runtime engine is appropriate for your use case and under what circumstances you may switch or even combine multiple runtimes in the same system.