ETCD
The CDL uses the etcd (an open-source key-value store) as the DB service discovery. When the CDL pods (Endpoint, Slot or Index) is started, killed or shutdown, it results in updating the event to etcd by publishing the state.
The CDL endpoint is interested in knowing when a Slot or Index pod comes up or goes down. Therefore, it subscribes to the notifications for Slot and Index pod events in etcd.
Similarly, the CDL Slot or Index pod is interested in knowing when its peer replica pod (with the same map-id) comes up or goes down. Therefore, it subscribes to the notifications for corresponding Slot or Index (with same map-id) pod events in etcd.
Thus, the notifications are sent to each of the pods subscribed to these events. In addition, when a key event is added or removed, it refreshes the local map. The etcd cache is only applicable for local site events.