Currently in ObserverReadProxyProvider#invoke, only when observerReadEnabled && isRead(method) is true, the code will check whether to talk to Observer. Otherwise always talk to active. The issue here is that currently it can only be set through setObserverReadEnabled, which is used by tests only. So observer read is always disabled in deployment and no way to enable it. We may want to either expose a configuration key, or hard code it to true so it can only be changed for testing purpose, or simply remove this variable. This is closely related to HDFS-13923.