Openshift interactive courses:
https://learn.openshift.com/
Kubernetes Interactive courses:
https://katacoda.com/courses/kubernetes
Kubernetes online playground:
https://labs.play-with-k8s.com/
Docker interactive courses:
https://katacoda.com/courses/docker
Container without docker interactive courses:
https://katacoda.com/courses/containers-without-docker
Istio interactive courses:
https://katacoda.com/courses/istio
https://learn.openshift.com/servicemesh/
Prometheus:
https://katacoda.com/courses/prometheus