Fallback to use the PD leader member info if it does not exist in etcd member list

[JmPotato]

From PD A:

[2024/01/21 01:51:07.255 +08:00] [INFO] [server.go:1434] ["start to watch pd leader"] [pd-leader="name:\"pd-{pd_b}-2379\" member_id:10281341235671451865 peer_urls:\"http://{pd_b}:2380\" client_urls:\"http://{pd_b}:2379\" "]

According to this log, it successfully watch and set the PD leader B at 01:51:07.255. However, from the client side:

[2024/01/21 01:51:47.495 +08:00] [INFO] [base_client.go:299] ["[pd] cannot update member from this address"] [address=http://{pd_a}:2379] [error="[PD:client:ErrClientGetLeader]get leader from leader address don't exist error"]

This means the following code failed to get the pdLeader from members though it has a PD leader set.

pd/server/grpc_service.go

Lines 495 to 501 in b27b1e9

	leader := s.member.GetLeader()
	for _, m := range members {
	if m.MemberId == leader.GetMemberId() {
	pdLeader = m
	break
	}
	}

Maybe we should fallback to use the PD leader member info if it does not exist in etcd member list.

[JmPotato]

The significant time difference between the two logs is because the physical time of the machine differs by 40 seconds. So this should not be a problem that needs to be fixed.