What is the difference between RoleBinding and ClusterRoleBinding? And what are the usages of them?
The Cluster variants apply to every namespace. The others only to the namespace they are in.
Please refer the Kubernetes documentation here
A Role always sets permissions within a particular namespace; when you create a Role, you have to specify the namespace it belongs in.
ClusterRole, by contrast, is a non-namespaced resource. The resources have different names (Role and ClusterRole) because a Kubernetes object always has to be either namespaced or not namespaced; it can’t be both.
A rolebinding is namespace scoped and clusterrolebinding is cluster scoped i.e across all namespace.
ClusterRoles and ClusterRoleBindings are useful in the following cases:
Give permissions for non-namespaced resources like nodes
Give permissions for resources in all the namespaces of a cluster
Give permissions for non-resource endpoints like /healthz
A RoleBinding can also reference a ClusterRole to grant the permissions defined in that ClusterRole to resources inside the RoleBinding's namespace. This kind of reference lets you define a set of common roles across your cluster, then reuse them within multiple namespaces.