Allow insecure gRPC connections for federated learning (#8181)

* Allow insecure gRPC connections for federated learning

* format

plugin/federated/engine_federated.cc

@@ -42,8 +42,13 @@ class FederatedEngine : public IEngine {
     }
     utils::Printf("Connecting to federated server %s, world size %d, rank %d",
                   server_address_.c_str(), world_size_, rank_);
-    client_.reset(new xgboost::federated::FederatedClient(server_address_, rank_, server_cert_,
-                                                          client_key_, client_cert_));
+    if (server_cert_.empty() || client_key_.empty() || client_cert_.empty()) {
+      utils::Printf("Certificates not specified, turning off SSL.");
+      client_.reset(new xgboost::federated::FederatedClient(server_address_, rank_));
+    } else {
+      client_.reset(new xgboost::federated::FederatedClient(server_address_, rank_, server_cert_,
+                                                            client_key_, client_cert_));
+    }
   }
 
   void Finalize() { client_.reset(); }
@@ -84,13 +89,9 @@ class FederatedEngine : public IEngine {
     }
   }
 
-  int LoadCheckPoint() override {
-    return 0;
-  }
+  int LoadCheckPoint() override { return 0; }
 
-  void CheckPoint() override {
-    version_number_ += 1;
-  }
+  void CheckPoint() override { version_number_ += 1; }
 
   int VersionNumber() const override { return version_number_; }
 

plugin/federated/federated_client.h

@@ -33,7 +33,7 @@ class FederatedClient {
         }()},
         rank_{rank} {}
 
-  /** @brief Insecure client for testing only. */
+  /** @brief Insecure client for connecting to localhost only. */
   FederatedClient(std::string const &server_address, int rank)
       : stub_{Federated::NewStub(
             grpc::CreateChannel(server_address, grpc::InsecureChannelCredentials()))},

plugin/federated/federated_server.cc

@@ -231,5 +231,20 @@ void RunServer(int port, int world_size, char const* server_key_file, char const
   server->Wait();
 }
 
+void RunInsecureServer(int port, int world_size) {
+  std::string const server_address = "0.0.0.0:" + std::to_string(port);
+  FederatedService service{world_size};
+
+  grpc::ServerBuilder builder;
+  builder.SetMaxReceiveMessageSize(std::numeric_limits<int>::max());
+  builder.AddListeningPort(server_address, grpc::InsecureServerCredentials());
+  builder.RegisterService(&service);
+  std::unique_ptr<grpc::Server> server(builder.BuildAndStart());
+  LOG(CONSOLE) << "Insecure federated server listening on " << server_address << ", world size "
+               << world_size;
+
+  server->Wait();
+}
+
 }  // namespace federated
 }  // namespace xgboost

plugin/federated/federated_server.h

@@ -40,5 +40,7 @@ class FederatedService final : public Federated::Service {
 void RunServer(int port, int world_size, char const* server_key_file, char const* server_cert_file,
                char const* client_cert_file);
 
+void RunInsecureServer(int port, int world_size);
+
 }  // namespace federated
 }  // namespace xgboost