Kubernetes Cluster Upgrade

• First stable version: v1.0 (July 2015)
• Kubernetes supports up to 3 versions at a time. E.g., 1.21, 1.20, 1.19

Compatibility

• kube-apiserver: must be the higher version of the control plane
• kube-controller-manager & kube-scheduler: can have up to 1 minor version lower
• kubelet & kube-proxy: can have up to 2 minor versions lower
• kubectl: can have any version

Upgrade Process

• The version must be upgraded one at time! (minor by minor)

• Steps

• Upgrade masters: upgrade the control plan

• Upgrade workers: upgrade one one by one or add nodes with newer version