Slot Replica Set Failure Call Flow
This section describes how the failover happens when two slot replicas that belong to the same replica set are down or unavailable.
The slot failure is an example of two points-of-failure scenario where the two slot replicas reside on different virtual machines or hosts.

Step |
Description |
---|---|
1 |
In the Site 1 environment, slot replica 1 and replica 2 for a configured shard is down or unavailable. Since both the replicas for the shard are unavailable, the CDL endpoint in Site 1 is shut down and all the subsequent requests are directed to the CDL endpoint on Site 2. In the Site 1 environment, the SMF sends a N7 Create request to PCF REST endpoint over the N7 interface. |
2 |
The PCF REST endpoint receives the request and forwards it to the PCF Engine. |
3 |
The PCF Engine attempts to connect the CDL endpoint to send the Session Create request. If the CDL endpoint is unreachable, the PCF Engine sorts the CDL points across Site 1 and Site 2 to recognize the endpoint with the highest rating or priority. |
4 |
The Create Request is evaluated in the stored session and the PCF Engine forwards the request to the CDL endpoint residing in Site 2. |
5 |
After the call request is successful, the PCF Engine notifies the Success message to the PCF REST endpoint. |
6 |
The PCF REST endpoint forwards the Success message to the SMF. |