A ServiceMeshMember resource can be created in a namespace for joining the namespace to mesh. It is safer than editing ServiceMeshMemberRoll in istio-system. ServiceMesh operator will automatically add namespace to the default ServiceMeshMemberRoll and corresponding policies when it sees a ServiceMeshMember in a namespace. Similarly, namespace will be removed from mesh when ServiceMeshMember resource is removed from namespace. ServiceMeshMember resource must be named default for it to work.
apiVersion: maistra.io/v1
kind: ServiceMeshMember
metadata:
name: default
namespace: <namespace>
spec:
controlPlaneRef:
name: basic
namespace: istio-system