gPRC authentication fails due to bad certificate

[namsral]

The gRPC gateway fails to authentication to the etcd server. The gRPC gateway can be used to support REST requests.

Logs from the etcd container in the etcd-0 pod:

WARNING: 2024/02/08 14:44:32 [core] grpc: addrConn.createTransport failed to connect to {0.0.0.0:2379 0.0.0.0:2379 <nil> 0 <nil>}. Err: connection error: desc = "transport: authentication handshake failed: remote error: tls: bad certificate". Reconnecting...
WARNING: 2024/02/08 14:46:27 [core] grpc: addrConn.createTransport failed to connect to {0.0.0.0:2379 0.0.0.0:2379 <nil> 0 <nil>}. Err: connection error: desc = "transport: authentication handshake failed: remote error: tls: bad certificate". Reconnecting...
WARNING: 2024/02/08 14:48:48 [core] grpc: addrConn.createTransport failed to connect to {0.0.0.0:2379 0.0.0.0:2379 <nil> 0 <nil>}. Err: connection error: desc = "transport: authentication handshake failed: remote error: tls: bad certificate". Reconnecting...
WARNING: 2024/02/08 14:50:56 [core] grpc: addrConn.createTransport failed to connect to {0.0.0.0:2379 0.0.0.0:2379 <nil> 0 <nil>}. Err: connection error: desc = "transport: authentication handshake failed: remote error: tls: bad certificate". Reconnecting...

If Gardener doesn't need to make REST request the gRPC can be disabled with the following flag --enable-grpc-gateway=false. If it does, it requires a proper client certificate instead of re-using the etchd server certificate.

More informartion about this issue, see etcd-io/etcd#15755