Refactor replication client/server (#1311)

src/query/interpreter.cpp

@@ -238,9 +238,10 @@ class ReplQueryHandler final : public query::ReplicationQueryHandler {
       if (!port || *port < 0 || *port > std::numeric_limits<uint16_t>::max()) {
         throw QueryRuntimeException("Port number invalid!");
       }
-      if (!db_->SetReplicaRole(
+      if (!db_->SetReplicaRole(storage::replication::ReplicationServerConfig{
-              io::network::Endpoint(storage::replication::kDefaultReplicationServerIp, static_cast<uint16_t>(*port)),
+              .ip_address = storage::replication::kDefaultReplicationServerIp,
-              storage::replication::ReplicationServerConfig{})) {
+              .port = static_cast<uint16_t>(*port),
+          })) {
         throw QueryRuntimeException("Couldn't set role to replica!");
       }
     }
@@ -286,9 +287,14 @@ class ReplQueryHandler final : public query::ReplicationQueryHandler {
         io::network::Endpoint::ParseSocketOrIpAddress(socket_address, storage::replication::kDefaultReplicationPort);
     if (maybe_ip_and_port) {
       auto [ip, port] = *maybe_ip_and_port;
-      auto ret = db_->RegisterReplica(name, {std::move(ip), port}, repl_mode,
+      auto ret = db_->RegisterReplica(
-                                      storage::replication::RegistrationMode::MUST_BE_INSTANTLY_VALID,
+          storage::replication::RegistrationMode::MUST_BE_INSTANTLY_VALID,
-                                      {.replica_check_frequency = replica_check_frequency, .ssl = std::nullopt});
+          storage::replication::ReplicationClientConfig{.name = name,
+                                                        .mode = repl_mode,
+                                                        .ip_address = ip,
+                                                        .port = port,
+                                                        .replica_check_frequency = replica_check_frequency,
+                                                        .ssl = std::nullopt});
       if (ret.HasError()) {
         throw QueryRuntimeException(fmt::format("Couldn't register replica '{}'!", name));
       }

src/storage/v2/disk/storage.hpp

@@ -375,13 +375,12 @@ class DiskStorage final : public Storage {
   EdgeImportMode edge_import_status_{EdgeImportMode::INACTIVE};
   std::unique_ptr<EdgeImportModeCache> edge_import_mode_cache_{nullptr};
 
-  auto CreateReplicationClient(std::string name, io::network::Endpoint endpoint, replication::ReplicationMode mode,
+  auto CreateReplicationClient(replication::ReplicationClientConfig const &config)
-                               const replication::ReplicationClientConfig &config)
       -> std::unique_ptr<ReplicationClient> override {
     throw utils::BasicException("Disk storage mode does not support replication.");
   }
 
-  auto CreateReplicationServer(io::network::Endpoint endpoint, const replication::ReplicationServerConfig &config)
+  auto CreateReplicationServer(const replication::ReplicationServerConfig &config)
       -> std::unique_ptr<ReplicationServer> override {
     throw utils::BasicException("Disk storage mode does not support replication.");
   }

src/storage/v2/inmemory/replication/replication_client.cpp

@@ -102,10 +102,9 @@ uint64_t ReplicateCurrentWal(CurrentWalHandler &stream, durability::WalFile cons
 
 ////// ReplicationClient //////
 
-InMemoryReplicationClient::InMemoryReplicationClient(InMemoryStorage *storage, std::string name,
+InMemoryReplicationClient::InMemoryReplicationClient(InMemoryStorage *storage,
-                                                     io::network::Endpoint endpoint, replication::ReplicationMode mode,
                                                      const replication::ReplicationClientConfig &config)
-    : ReplicationClient{storage, std::move(name), std::move(endpoint), mode, config} {}
+    : ReplicationClient{storage, config} {}
 
 void InMemoryReplicationClient::RecoverReplica(uint64_t replica_commit) {
   spdlog::debug("Starting replica recover");

src/storage/v2/inmemory/replication/replication_client.hpp

@@ -18,8 +18,7 @@ class InMemoryStorage;
 
 class InMemoryReplicationClient : public ReplicationClient {
  public:
-  InMemoryReplicationClient(InMemoryStorage *storage, std::string name, io::network::Endpoint endpoint,
+  InMemoryReplicationClient(InMemoryStorage *storage, const replication::ReplicationClientConfig &config);
-                            replication::ReplicationMode mode, const replication::ReplicationClientConfig &config = {});
 
  protected:
   void RecoverReplica(uint64_t replica_commit) override;

src/storage/v2/inmemory/replication/replication_server.cpp

@@ -32,9 +32,9 @@ std::pair<uint64_t, durability::WalDeltaData> ReadDelta(durability::BaseDecoder
 };
 }  // namespace
 
-InMemoryReplicationServer::InMemoryReplicationServer(InMemoryStorage *storage, memgraph::io::network::Endpoint endpoint,
+InMemoryReplicationServer::InMemoryReplicationServer(InMemoryStorage *storage,
                                                      const replication::ReplicationServerConfig &config)
-    : ReplicationServer{std::move(endpoint), config}, storage_(storage) {
+    : ReplicationServer{config}, storage_(storage) {
   rpc_server_.Register<replication::HeartbeatRpc>([this](auto *req_reader, auto *res_builder) {
     spdlog::debug("Received HeartbeatRpc");
     this->HeartbeatHandler(req_reader, res_builder);

src/storage/v2/inmemory/replication/replication_server.hpp

@@ -20,8 +20,7 @@ class InMemoryStorage;
 
 class InMemoryReplicationServer : public ReplicationServer {
  public:
-  explicit InMemoryReplicationServer(InMemoryStorage *storage, io::network::Endpoint endpoint,
+  explicit InMemoryReplicationServer(InMemoryStorage *storage, const replication::ReplicationServerConfig &config);
-                                     const replication::ReplicationServerConfig &config);
 
  private:
   // RPC handlers

src/storage/v2/inmemory/storage.cpp

@@ -1832,16 +1832,14 @@ utils::FileRetainer::FileLockerAccessor::ret_type InMemoryStorage::UnlockPath()
   return true;
 }
 
-auto InMemoryStorage::CreateReplicationClient(std::string name, io::network::Endpoint endpoint,
+auto InMemoryStorage::CreateReplicationClient(replication::ReplicationClientConfig const &config)
-                                              replication::ReplicationMode mode,
-                                              replication::ReplicationClientConfig const &config)
     -> std::unique_ptr<ReplicationClient> {
-  return std::make_unique<InMemoryReplicationClient>(this, std::move(name), std::move(endpoint), mode, config);
+  return std::make_unique<InMemoryReplicationClient>(this, config);
 }
 
 std::unique_ptr<ReplicationServer> InMemoryStorage::CreateReplicationServer(
-    io::network::Endpoint endpoint, const replication::ReplicationServerConfig &config) {
+    const replication::ReplicationServerConfig &config) {
-  return std::make_unique<InMemoryReplicationServer>(this, std::move(endpoint), config);
+  return std::make_unique<InMemoryReplicationServer>(this, config);
 }
 
 }  // namespace memgraph::storage

src/storage/v2/inmemory/storage.hpp

@@ -371,11 +371,10 @@ class InMemoryStorage final : public Storage {
 
   Transaction CreateTransaction(IsolationLevel isolation_level, StorageMode storage_mode) override;
 
-  auto CreateReplicationClient(std::string name, io::network::Endpoint endpoint, replication::ReplicationMode mode,
+  auto CreateReplicationClient(replication::ReplicationClientConfig const &config)
-                               replication::ReplicationClientConfig const &config)
       -> std::unique_ptr<ReplicationClient> override;
 
-  auto CreateReplicationServer(io::network::Endpoint endpoint, const replication::ReplicationServerConfig &config)
+  auto CreateReplicationServer(const replication::ReplicationServerConfig &config)
       -> std::unique_ptr<ReplicationServer> override;
 
  private:

src/storage/v2/replication/config.hpp

@@ -1,4 +1,4 @@
-// Copyright 2022 Memgraph Ltd.
+// Copyright 2023 Memgraph Ltd.
 //
 // Use of this software is governed by the Business Source License
 // included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
@@ -15,8 +15,15 @@
 #include <optional>
 #include <string>
 
+#include "storage/v2/replication/enums.hpp"
+
 namespace memgraph::storage::replication {
 struct ReplicationClientConfig {
+  std::string name;
+  ReplicationMode mode;
+  std::string ip_address;
+  uint16_t port;
+
   // The default delay between main checking/pinging replicas is 1s because
   // that seems like a reasonable timeframe in which main should notice a
   // replica is down.
@@ -33,6 +40,8 @@ struct ReplicationClientConfig {
 };
 
 struct ReplicationServerConfig {
+  std::string ip_address;
+  uint16_t port;
   struct SSL {
     std::string key_file;
     std::string cert_file;

src/storage/v2/replication/replication.cpp

@@ -23,8 +23,8 @@ using OOMExceptionEnabler = utils::MemoryTracker::OutOfMemoryExceptionEnabler;
 
 namespace {
 
-std::string RegisterReplicaErrorToString(ReplicationState::RegisterReplicaError error) {
+std::string RegisterReplicaErrorToString(RegisterReplicaError error) {
-  using enum ReplicationState::RegisterReplicaError;
+  using enum RegisterReplicaError;
   switch (error) {
     case NAME_EXISTS:
       return "NAME_EXISTS";
@@ -147,84 +147,75 @@ bool storage::ReplicationState::FinalizeTransaction(uint64_t timestamp) {
   return finalized_on_all_replicas;
 }
 
-utils::BasicResult<ReplicationState::RegisterReplicaError> ReplicationState::RegisterReplica(
+utils::BasicResult<RegisterReplicaError> ReplicationState::RegisterReplica(
-    std::string name, io::network::Endpoint endpoint, const replication::ReplicationMode replication_mode,
     const replication::RegistrationMode registration_mode, const replication::ReplicationClientConfig &config,
     Storage *storage) {
   MG_ASSERT(GetRole() == replication::ReplicationRole::MAIN, "Only main instance can register a replica!");
 
-  const bool name_exists = replication_clients_.WithLock([&](auto &clients) {
+  auto name_check = [&config](auto &clients) {
-    return std::any_of(clients.begin(), clients.end(), [&name](const auto &client) { return client->Name() == name; });
+    auto name_matches = [&name = config.name](const auto &client) { return client->Name() == name; };
-  });
+    return std::any_of(clients.begin(), clients.end(), name_matches);
+  };
 
-  if (name_exists) {
+  auto desired_endpoint = io::network::Endpoint{config.ip_address, config.port};
-    return RegisterReplicaError::NAME_EXISTS;
+  auto endpoint_check = [&](auto &clients) {
-  }
+    auto endpoint_matches = [&](const auto &client) { return client->Endpoint() == desired_endpoint; };
+    return std::any_of(clients.begin(), clients.end(), endpoint_matches);
+  };
 
-  const auto end_point_exists = replication_clients_.WithLock([&endpoint](auto &clients) {
+  auto task = [&](auto &clients) -> utils::BasicResult<RegisterReplicaError> {
-    return std::any_of(clients.begin(), clients.end(),
+    if (name_check(clients)) {
-                       [&endpoint](const auto &client) { return client->Endpoint() == endpoint; });
+      return RegisterReplicaError::NAME_EXISTS;
-  });
+    }
 
-  if (end_point_exists) {
+    if (endpoint_check(clients)) {
-    return RegisterReplicaError::END_POINT_EXISTS;
+      return RegisterReplicaError::END_POINT_EXISTS;
-  }
+    }
 
-  if (ShouldStoreAndRestoreReplicationState()) {
+    if (!TryPersistReplicaClient(config)) {
-    auto data = replication::ReplicationStatusToJSON(
-        replication::ReplicationStatus{.name = name,
-                                       .ip_address = endpoint.address,
-                                       .port = endpoint.port,
-                                       .sync_mode = replication_mode,
-                                       .replica_check_frequency = config.replica_check_frequency,
-                                       .ssl = config.ssl,
-                                       .role = replication::ReplicationRole::REPLICA});
-    if (!durability_->Put(name, data.dump())) {
-      spdlog::error("Error when saving replica {} in settings.", name);
       return RegisterReplicaError::COULD_NOT_BE_PERSISTED;
     }
-  }
 
-  auto client = storage->CreateReplicationClient(std::move(name), std::move(endpoint), replication_mode, config);
+    auto client = storage->CreateReplicationClient(config);
-  client->Start();
+    client->Start();
 
-  if (client->State() == replication::ReplicaState::INVALID) {
+    if (client->State() == replication::ReplicaState::INVALID) {
-    if (replication::RegistrationMode::CAN_BE_INVALID != registration_mode) {
+      if (replication::RegistrationMode::CAN_BE_INVALID != registration_mode) {
-      return RegisterReplicaError::CONNECTION_FAILED;
+        return RegisterReplicaError::CONNECTION_FAILED;
+      }
+
+      spdlog::warn("Connection failed when registering replica {}. Replica will still be registered.", client->Name());
     }
 
-    spdlog::warn("Connection failed when registering replica {}. Replica will still be registered.", client->Name());
+    clients.push_back(std::move(client));
-  }
+    return {};
+  };
 
-  return replication_clients_.WithLock(
+  return replication_clients_.WithLock(task);
-      [&](auto &clients) -> utils::BasicResult<ReplicationState::RegisterReplicaError> {
-        // Another thread could have added a client with same name while
-        // we were connecting to this client.
-        if (std::any_of(clients.begin(), clients.end(),
-                        [&](const auto &other_client) { return client->Name() == other_client->Name(); })) {
-          return RegisterReplicaError::NAME_EXISTS;
-        }
-
-        if (std::any_of(clients.begin(), clients.end(), [&client](const auto &other_client) {
-              return client->Endpoint() == other_client->Endpoint();
-            })) {
-          return RegisterReplicaError::END_POINT_EXISTS;
-        }
-
-        clients.push_back(std::move(client));
-        return {};
-      });
 }
 
-bool ReplicationState::SetReplicaRole(io::network::Endpoint endpoint,
+bool ReplicationState::TryPersistReplicaClient(const replication::ReplicationClientConfig &config) {
-                                      const replication::ReplicationServerConfig &config, Storage *storage) {
+  if (!ShouldStoreAndRestoreReplicationState()) return true;
+  auto data = replication::ReplicationStatusToJSON(
+      replication::ReplicationStatus{.name = config.name,
+                                     .ip_address = config.ip_address,
+                                     .port = config.port,
+                                     .sync_mode = config.mode,
+                                     .replica_check_frequency = config.replica_check_frequency,
+                                     .ssl = config.ssl,
+                                     .role = replication::ReplicationRole::REPLICA});
+  if (durability_->Put(config.name, data.dump())) return true;
+  spdlog::error("Error when saving replica {} in settings.", config.name);
+  return false;
+}
+
+bool ReplicationState::SetReplicaRole(const replication::ReplicationServerConfig &config, Storage *storage) {
   // We don't want to restart the server if we're already a REPLICA
   if (GetRole() == replication::ReplicationRole::REPLICA) {
     return false;
   }
 
-  auto port = endpoint.port;  // assigning because we will move the endpoint
+  replication_server_ = storage->CreateReplicationServer(config);
-  replication_server_ = storage->CreateReplicationServer(std::move(endpoint), config);
   bool res = replication_server_->Start();
   if (!res) {
     spdlog::error("Unable to start the replication server.");
@@ -235,8 +226,8 @@ bool ReplicationState::SetReplicaRole(io::network::Endpoint endpoint,
     // Only thing that matters here is the role saved as REPLICA and the listening port
     auto data = replication::ReplicationStatusToJSON(
         replication::ReplicationStatus{.name = replication::kReservedReplicationRoleName,
-                                       .ip_address = "",
+                                       .ip_address = config.ip_address,
-                                       .port = port,
+                                       .port = config.port,
                                        .sync_mode = replication::ReplicationMode::SYNC,
                                        .replica_check_frequency = std::chrono::seconds(0),
                                        .ssl = std::nullopt,
@@ -318,8 +309,10 @@ void ReplicationState::RestoreReplicationRole(Storage *storage) {
   }
 
   if (GetRole() == replication::ReplicationRole::REPLICA) {
-    io::network::Endpoint endpoint(replication::kDefaultReplicationServerIp, port);
+    replication_server_ = storage->CreateReplicationServer(replication::ReplicationServerConfig{
-    replication_server_ = storage->CreateReplicationServer(std::move(endpoint), {});
+        .ip_address = replication::kDefaultReplicationServerIp,
+        .port = port,
+    });
     bool res = replication_server_->Start();
     if (!res) {
       LOG_FATAL("Unable to start the replication server.");
@@ -352,14 +345,16 @@ void ReplicationState::RestoreReplicas(Storage *storage) {
       continue;
     }
 
-    auto ret =
+    auto ret = RegisterReplica(replication::RegistrationMode::CAN_BE_INVALID,
-        RegisterReplica(std::move(replica_status.name), {std::move(replica_status.ip_address), replica_status.port},
+                               replication::ReplicationClientConfig{
-                        replica_status.sync_mode, replication::RegistrationMode::CAN_BE_INVALID,
+                                   .name = replica_status.name,
-                        {
+                                   .mode = replica_status.sync_mode,
-                            .replica_check_frequency = replica_status.replica_check_frequency,
+                                   .ip_address = replica_status.ip_address,
-                            .ssl = replica_status.ssl,
+                                   .port = replica_status.port,
-                        },
+                                   .replica_check_frequency = replica_status.replica_check_frequency,
-                        storage);
+                                   .ssl = replica_status.ssl,
+                               },
+                               storage);
 
     if (ret.HasError()) {
       MG_ASSERT(RegisterReplicaError::CONNECTION_FAILED != ret.GetError());

src/storage/v2/replication/replication.hpp

@@ -32,14 +32,9 @@ class Storage;
 class ReplicationServer;
 class ReplicationClient;
 
-struct ReplicationState {
+enum class RegisterReplicaError : uint8_t { NAME_EXISTS, END_POINT_EXISTS, CONNECTION_FAILED, COULD_NOT_BE_PERSISTED };
-  enum class RegisterReplicaError : uint8_t {
-    NAME_EXISTS,
-    END_POINT_EXISTS,
-    CONNECTION_FAILED,
-    COULD_NOT_BE_PERSISTED
-  };
 
+struct ReplicationState {
   // TODO: This mirrors the logic in InMemoryConstructor; make it independent
   ReplicationState(bool restore, std::filesystem::path durability_dir);
 
@@ -50,7 +45,7 @@ struct ReplicationState {
 
   bool SetMainReplicationRole(Storage *storage);  // Set the instance to MAIN
   // TODO: ReplicationServer/Client uses Storage* for RPC callbacks
-  bool SetReplicaRole(io::network::Endpoint endpoint, const replication::ReplicationServerConfig &config,
+  bool SetReplicaRole(const replication::ReplicationServerConfig &config,
                       Storage *storage);  // Sets the instance to REPLICA
   // Generic restoration
   void RestoreReplicationRole(Storage *storage);
@@ -64,9 +59,7 @@ struct ReplicationState {
   bool FinalizeTransaction(uint64_t timestamp);
 
   // MAIN connecting to replicas
-  utils::BasicResult<RegisterReplicaError> RegisterReplica(std::string name, io::network::Endpoint endpoint,
+  utils::BasicResult<RegisterReplicaError> RegisterReplica(const replication::RegistrationMode registration_mode,
-                                                           const replication::ReplicationMode replication_mode,
-                                                           const replication::RegistrationMode registration_mode,
                                                            const replication::ReplicationClientConfig &config,
                                                            Storage *storage);
   bool UnregisterReplica(std::string_view name);
@@ -97,8 +90,8 @@ struct ReplicationState {
   void AppendEpoch(std::string new_epoch);
 
  private:
+  bool TryPersistReplicaClient(const replication::ReplicationClientConfig &config);
   bool ShouldStoreAndRestoreReplicationState() const { return nullptr != durability_; }
-
   void SetRole(replication::ReplicationRole role) { return replication_role_.store(role); }
 
   // NOTE: Server is not in MAIN it is in REPLICA

src/storage/v2/replication/replication_client.cpp

@@ -30,14 +30,12 @@ static auto CreateClientContext(const replication::ReplicationClientConfig &conf
                       : communication::ClientContext{};
 }
 
-ReplicationClient::ReplicationClient(Storage *storage, std::string name, memgraph::io::network::Endpoint endpoint,
+ReplicationClient::ReplicationClient(Storage *storage, replication::ReplicationClientConfig const &config)
-                                     replication::ReplicationMode mode,
+    : name_{config.name},
-                                     replication::ReplicationClientConfig const &config)
-    : name_{std::move(name)},
       rpc_context_{CreateClientContext(config)},
-      rpc_client_{std::move(endpoint), &rpc_context_},
+      rpc_client_{io::network::Endpoint(config.ip_address, config.port), &rpc_context_},
       replica_check_frequency_{config.replica_check_frequency},
-      mode_{mode},
+      mode_{config.mode},
       storage_{storage} {}
 
 ReplicationClient::~ReplicationClient() {

src/storage/v2/replication/replication_client.hpp

@@ -66,8 +66,7 @@ class ReplicationClient {
   friend class ReplicaStream;
 
  public:
-  ReplicationClient(Storage *storage, std::string name, memgraph::io::network::Endpoint endpoint,
+  ReplicationClient(Storage *storage, replication::ReplicationClientConfig const &config);
-                    replication::ReplicationMode mode, const replication::ReplicationClientConfig &config);
 
   ReplicationClient(ReplicationClient const &) = delete;
   ReplicationClient &operator=(ReplicationClient const &) = delete;

src/storage/v2/replication/replication_server.cpp

@@ -30,9 +30,10 @@ auto CreateServerContext(const replication::ReplicationServerConfig &config) ->
 constexpr auto kReplictionServerThreads = 1;
 }  // namespace
 
-ReplicationServer::ReplicationServer(io::network::Endpoint endpoint, const replication::ReplicationServerConfig &config)
+ReplicationServer::ReplicationServer(const replication::ReplicationServerConfig &config)
     : rpc_server_context_{CreateServerContext(config)},
-      rpc_server_{std::move(endpoint), &rpc_server_context_, kReplictionServerThreads} {
+      rpc_server_{io::network::Endpoint{config.ip_address, config.port}, &rpc_server_context_,
+                  kReplictionServerThreads} {
   rpc_server_.Register<replication::FrequentHeartbeatRpc>([](auto *req_reader, auto *res_builder) {
     spdlog::debug("Received FrequentHeartbeatRpc");
     FrequentHeartbeatHandler(req_reader, res_builder);

src/storage/v2/replication/replication_server.hpp

@@ -20,7 +20,7 @@ namespace memgraph::storage {
 
 class ReplicationServer {
  public:
-  explicit ReplicationServer(io::network::Endpoint endpoint, const replication::ReplicationServerConfig &config);
+  explicit ReplicationServer(const replication::ReplicationServerConfig &config);
   ReplicationServer(const ReplicationServer &) = delete;
   ReplicationServer(ReplicationServer &&) = delete;
   ReplicationServer &operator=(const ReplicationServer &) = delete;

src/storage/v2/storage.hpp

@@ -315,29 +315,23 @@ class Storage {
 
   virtual void EstablishNewEpoch() = 0;
 
-  virtual auto CreateReplicationClient(std::string name, io::network::Endpoint endpoint,
+  virtual auto CreateReplicationClient(replication::ReplicationClientConfig const &config)
-                                       replication::ReplicationMode mode,
-                                       replication::ReplicationClientConfig const &config)
       -> std::unique_ptr<ReplicationClient> = 0;
 
-  virtual auto CreateReplicationServer(io::network::Endpoint endpoint,
+  virtual auto CreateReplicationServer(const replication::ReplicationServerConfig &config)
-                                       replication::ReplicationServerConfig const &config)
       -> std::unique_ptr<ReplicationServer> = 0;
 
   /// REPLICATION
-  bool SetReplicaRole(io::network::Endpoint endpoint, const replication::ReplicationServerConfig &config) {
+  bool SetReplicaRole(const replication::ReplicationServerConfig &config) {
-    return replication_state_.SetReplicaRole(std::move(endpoint), config, this);
+    return replication_state_.SetReplicaRole(config, this);
   }
   bool SetMainReplicationRole() { return replication_state_.SetMainReplicationRole(this); }
 
   /// @pre The instance should have a MAIN role
   /// @pre Timeout can only be set for SYNC replication
-  auto RegisterReplica(std::string name, io::network::Endpoint endpoint,
+  auto RegisterReplica(const replication::RegistrationMode registration_mode,
-                       const replication::ReplicationMode replication_mode,
-                       const replication::RegistrationMode registration_mode,
                        const replication::ReplicationClientConfig &config) {
-    return replication_state_.RegisterReplica(std::move(name), std::move(endpoint), replication_mode, registration_mode,
+    return replication_state_.RegisterReplica(registration_mode, config, this);
-                                              config, this);
   }
   /// @pre The instance should have a MAIN role
   bool UnregisterReplica(const std::string &name) { return replication_state_.UnregisterReplica(name); }