Does Kubernetes installation always needs Docker?
Historically, kubernetes only had support for docker as the container runtime.
A second option was added (not sure which version) to use rkt as the runtime instead of docker.
As of version 1.9, OCI (open container initiative) runtimes support has been added in beta, allowing for a whole list of new container runtimes to be supported such as:
- bwrap-oci
- crun
- railcar
- rkt
- runc
- runxlc
So the answers are:
1) no, if you choose kubernetes > 1.9 you can choose from a variety of container runtimes
2) yes, kubernetes 1.9+ has cri-o support
3) see the list above
A more detailed explanation here: https://joejulian.name/post/kubernetes-container-engine-comparison/