1 files changed, 318 insertions, 193 deletions

diff --git a/grpc/src/core/ext/filters/client_channel/lb_policy/xds/cds.cc b/grpc/src/core/ext/filters/client_channel/lb_policy/xds/cds.cc
index 8a10db52..49bff276 100644
--- a/grpc/src/core/ext/filters/client_channel/lb_policy/xds/cds.cc
+++ b/grpc/src/core/ext/filters/client_channel/lb_policy/xds/cds.cc
@@ -63,40 +63,55 @@ class CdsLb : public LoadBalancingPolicy {
 
   void UpdateLocked(UpdateArgs args) override;
   void ResetBackoffLocked() override;
+  void ExitIdleLocked() override;
 
  private:
   // Watcher for getting cluster data from XdsClient.
   class ClusterWatcher : public XdsClient::ClusterWatcherInterface {
    public:
-    explicit ClusterWatcher(RefCountedPtr<CdsLb> parent)
-        : parent_(std::move(parent)) {}
+    ClusterWatcher(RefCountedPtr<CdsLb> parent, std::string name)
+        : parent_(std::move(parent)), name_(std::move(name)) {}
 
     void OnClusterChanged(XdsApi::CdsUpdate cluster_data) override {
-      new Notifier(parent_, std::move(cluster_data));
+      new Notifier(parent_, name_, std::move(cluster_data));
     }
-    void OnError(grpc_error* error) override { new Notifier(parent_, error); }
-    void OnResourceDoesNotExist() override { new Notifier(parent_); }
+    void OnError(grpc_error_handle error) override {
+      new Notifier(parent_, name_, error);
+    }
+    void OnResourceDoesNotExist() override { new Notifier(parent_, name_); }
 
    private:
     class Notifier {
      public:
-      Notifier(RefCountedPtr<CdsLb> parent, XdsApi::CdsUpdate update);
-      Notifier(RefCountedPtr<CdsLb> parent, grpc_error* error);
-      explicit Notifier(RefCountedPtr<CdsLb> parent);
+      Notifier(RefCountedPtr<CdsLb> parent, std::string name,
+               XdsApi::CdsUpdate update);
+      Notifier(RefCountedPtr<CdsLb> parent, std::string name,
+               grpc_error_handle error);
+      explicit Notifier(RefCountedPtr<CdsLb> parent, std::string name);
 
      private:
       enum Type { kUpdate, kError, kDoesNotExist };
 
-      static void RunInExecCtx(void* arg, grpc_error* error);
-      void RunInWorkSerializer(grpc_error* error);
+      static void RunInExecCtx(void* arg, grpc_error_handle error);
+      void RunInWorkSerializer(grpc_error_handle error);
 
       RefCountedPtr<CdsLb> parent_;
+      std::string name_;
       grpc_closure closure_;
       XdsApi::CdsUpdate update_;
       Type type_;
     };
 
     RefCountedPtr<CdsLb> parent_;
+    std::string name_;
+  };
+
+  struct WatcherState {
+    // Pointer to watcher, to be used when cancelling.
+    // Not owned, so do not dereference.
+    ClusterWatcher* watcher = nullptr;
+    // Most recent update obtained from this watcher.
+    absl::optional<XdsApi::CdsUpdate> update;
   };
 
   // Delegating helper to be passed to child policy.
@@ -119,12 +134,20 @@ class CdsLb : public LoadBalancingPolicy {
 
   void ShutdownLocked() override;
 
-  void OnClusterChanged(XdsApi::CdsUpdate cluster_data);
-  void OnError(grpc_error* error);
-  void OnResourceDoesNotExist();
+  bool GenerateDiscoveryMechanismForCluster(
+      const std::string& name, Json::Array* discovery_mechanisms,
+      std::set<std::string>* clusters_needed);
+  void OnClusterChanged(const std::string& name,
+                        XdsApi::CdsUpdate cluster_data);
+  void OnError(const std::string& name, grpc_error_handle error);
+  void OnResourceDoesNotExist(const std::string& name);
 
-  grpc_error* UpdateXdsCertificateProvider(
-      const XdsApi::CdsUpdate& cluster_data);
+  grpc_error_handle UpdateXdsCertificateProvider(
+      const std::string& cluster_name, const XdsApi::CdsUpdate& cluster_data);
+
+  void CancelClusterDataWatch(absl::string_view cluster_name,
+                              XdsClient::ClusterWatcherInterface* watcher,
+                              bool delay_unsubscription = false);
 
   void MaybeDestroyChildPolicyLocked();
 
@@ -135,9 +158,10 @@ class CdsLb : public LoadBalancingPolicy {
 
   // The xds client.
   RefCountedPtr<XdsClient> xds_client_;
-  // A pointer to the cluster watcher, to be used when cancelling the watch.
-  // Note that this is not owned, so this pointer must never be derefernced.
-  ClusterWatcher* cluster_watcher_ = nullptr;
+
+  // Maps from cluster name to the state for that cluster.
+  // The root of the tree is config_->cluster().
+  std::map<std::string, WatcherState> watchers_;
 
   RefCountedPtr<grpc_tls_certificate_provider> root_certificate_provider_;
   RefCountedPtr<grpc_tls_certificate_provider> identity_certificate_provider_;
@@ -155,43 +179,50 @@ class CdsLb : public LoadBalancingPolicy {
 //
 
 CdsLb::ClusterWatcher::Notifier::Notifier(RefCountedPtr<CdsLb> parent,
+                                          std::string name,
                                           XdsApi::CdsUpdate update)
-    : parent_(std::move(parent)), update_(std::move(update)), type_(kUpdate) {
+    : parent_(std::move(parent)),
+      name_(std::move(name)),
+      update_(std::move(update)),
+      type_(kUpdate) {
   GRPC_CLOSURE_INIT(&closure_, &RunInExecCtx, this, nullptr);
   ExecCtx::Run(DEBUG_LOCATION, &closure_, GRPC_ERROR_NONE);
 }
 
 CdsLb::ClusterWatcher::Notifier::Notifier(RefCountedPtr<CdsLb> parent,
-                                          grpc_error* error)
-    : parent_(std::move(parent)), type_(kError) {
+                                          std::string name,
+                                          grpc_error_handle error)
+    : parent_(std::move(parent)), name_(std::move(name)), type_(kError) {
   GRPC_CLOSURE_INIT(&closure_, &RunInExecCtx, this, nullptr);
   ExecCtx::Run(DEBUG_LOCATION, &closure_, error);
 }
 
-CdsLb::ClusterWatcher::Notifier::Notifier(RefCountedPtr<CdsLb> parent)
-    : parent_(std::move(parent)), type_(kDoesNotExist) {
+CdsLb::ClusterWatcher::Notifier::Notifier(RefCountedPtr<CdsLb> parent,
+                                          std::string name)
+    : parent_(std::move(parent)), name_(std::move(name)), type_(kDoesNotExist) {
   GRPC_CLOSURE_INIT(&closure_, &RunInExecCtx, this, nullptr);
   ExecCtx::Run(DEBUG_LOCATION, &closure_, GRPC_ERROR_NONE);
 }
 
 void CdsLb::ClusterWatcher::Notifier::RunInExecCtx(void* arg,
-                                                   grpc_error* error) {
+                                                   grpc_error_handle error) {
   Notifier* self = static_cast<Notifier*>(arg);
   GRPC_ERROR_REF(error);
   self->parent_->work_serializer()->Run(
       [self, error]() { self->RunInWorkSerializer(error); }, DEBUG_LOCATION);
 }
 
-void CdsLb::ClusterWatcher::Notifier::RunInWorkSerializer(grpc_error* error) {
+void CdsLb::ClusterWatcher::Notifier::RunInWorkSerializer(
+    grpc_error_handle error) {
   switch (type_) {
     case kUpdate:
-      parent_->OnClusterChanged(std::move(update_));
+      parent_->OnClusterChanged(name_, std::move(update_));
       break;
     case kError:
-      parent_->OnError(error);
+      parent_->OnError(name_, error);
       break;
     case kDoesNotExist:
-      parent_->OnResourceDoesNotExist();
+      parent_->OnResourceDoesNotExist(name_);
       break;
   };
   delete this;
@@ -261,13 +292,15 @@ void CdsLb::ShutdownLocked() {
   shutting_down_ = true;
   MaybeDestroyChildPolicyLocked();
   if (xds_client_ != nullptr) {
-    if (cluster_watcher_ != nullptr) {
+    for (auto& watcher : watchers_) {
       if (GRPC_TRACE_FLAG_ENABLED(grpc_cds_lb_trace)) {
         gpr_log(GPR_INFO, "[cdslb %p] cancelling watch for cluster %s", this,
-                config_->cluster().c_str());
+                watcher.first.c_str());
       }
-      xds_client_->CancelClusterDataWatch(config_->cluster(), cluster_watcher_);
+      CancelClusterDataWatch(watcher.first, watcher.second.watcher,
+                             /*delay_unsubscription=*/false);
     }
+    watchers_.clear();
     xds_client_.reset(DEBUG_LOCATION, "CdsLb");
   }
   grpc_channel_args_destroy(args_);
@@ -286,6 +319,10 @@ void CdsLb::ResetBackoffLocked() {
   if (child_policy_ != nullptr) child_policy_->ResetBackoffLocked();
 }
 
+void CdsLb::ExitIdleLocked() {
+  if (child_policy_ != nullptr) child_policy_->ExitIdleLocked();
+}
+
 void CdsLb::UpdateLocked(UpdateArgs args) {
   // Update config.
   auto old_config = std::move(config_);
@@ -301,119 +338,214 @@ void CdsLb::UpdateLocked(UpdateArgs args) {
   // If cluster name changed, cancel watcher and restart.
   if (old_config == nullptr || old_config->cluster() != config_->cluster()) {
     if (old_config != nullptr) {
-      if (GRPC_TRACE_FLAG_ENABLED(grpc_cds_lb_trace)) {
-        gpr_log(GPR_INFO, "[cdslb %p] cancelling watch for cluster %s", this,
-                old_config->cluster().c_str());
+      for (auto& watcher : watchers_) {
+        if (GRPC_TRACE_FLAG_ENABLED(grpc_cds_lb_trace)) {
+          gpr_log(GPR_INFO, "[cdslb %p] cancelling watch for cluster %s", this,
+                  watcher.first.c_str());
+        }
+        CancelClusterDataWatch(watcher.first, watcher.second.watcher,
+                               /*delay_unsubscription=*/true);
       }
-      xds_client_->CancelClusterDataWatch(old_config->cluster(),
-                                          cluster_watcher_,
-                                          /*delay_unsubscription=*/true);
+      watchers_.clear();
     }
-    if (GRPC_TRACE_FLAG_ENABLED(grpc_cds_lb_trace)) {
-      gpr_log(GPR_INFO, "[cdslb %p] starting watch for cluster %s", this,
-              config_->cluster().c_str());
-    }
-    auto watcher = absl::make_unique<ClusterWatcher>(Ref());
-    cluster_watcher_ = watcher.get();
+    auto watcher = absl::make_unique<ClusterWatcher>(Ref(), config_->cluster());
+    watchers_[config_->cluster()].watcher = watcher.get();
     xds_client_->WatchClusterData(config_->cluster(), std::move(watcher));
   }
 }
 
-void CdsLb::OnClusterChanged(XdsApi::CdsUpdate cluster_data) {
-  if (GRPC_TRACE_FLAG_ENABLED(grpc_cds_lb_trace)) {
-    gpr_log(GPR_INFO, "[cdslb %p] received CDS update from xds client %p: %s",
-            this, xds_client_.get(), cluster_data.ToString().c_str());
+// This method will attempt to generate one or multiple entries of discovery
+// mechanism recursively:
+// For cluster types EDS or LOGICAL_DNS, one discovery mechanism entry may be
+// generated cluster name, type and other data from the CdsUpdate inserted into
+// the entry and the entry appended to the array of entries.
+// Note, discovery mechanism entry can be generated if an CdsUpdate is
+// available; otherwise, just return false. For cluster type AGGREGATE,
+// recursively call the method for each child cluster.
+bool CdsLb::GenerateDiscoveryMechanismForCluster(
+    const std::string& name, Json::Array* discovery_mechanisms,
+    std::set<std::string>* clusters_needed) {
+  clusters_needed->insert(name);
+  auto& state = watchers_[name];
+  // Create a new watcher if needed.
+  if (state.watcher == nullptr) {
+    auto watcher = absl::make_unique<ClusterWatcher>(Ref(), name);
+    if (GRPC_TRACE_FLAG_ENABLED(grpc_cds_lb_trace)) {
+      gpr_log(GPR_INFO, "[cdslb %p] starting watch for cluster %s", this,
+              name.c_str());
+    }
+    state.watcher = watcher.get();
+    xds_client_->WatchClusterData(name, std::move(watcher));
+    return false;
   }
-  grpc_error* error = GRPC_ERROR_NONE;
-  error = UpdateXdsCertificateProvider(cluster_data);
-  if (error != GRPC_ERROR_NONE) {
-    return OnError(error);
+  // Don't have the update we need yet.
+  if (!state.update.has_value()) return false;
+  // For AGGREGATE clusters, recursively expand to child clusters.
+  if (state.update->cluster_type == XdsApi::CdsUpdate::ClusterType::AGGREGATE) {
+    bool missing_cluster = false;
+    for (const std::string& child_name :
+         state.update->prioritized_cluster_names) {
+      if (!GenerateDiscoveryMechanismForCluster(
+              child_name, discovery_mechanisms, clusters_needed)) {
+        missing_cluster = true;
+      }
+    }
+    return !missing_cluster;
+  }
+  std::string type;
+  switch (state.update->cluster_type) {
+    case XdsApi::CdsUpdate::ClusterType::EDS:
+      type = "EDS";
+      break;
+    case XdsApi::CdsUpdate::ClusterType::LOGICAL_DNS:
+      type = "LOGICAL_DNS";
+      break;
+    default:
+      GPR_ASSERT(0);
+      break;
   }
-  // Construct config for child policy.
-  Json::Object discovery_mechanism = {
-      {"clusterName", config_->cluster()},
-      {"max_concurrent_requests", cluster_data.max_concurrent_requests},
-      {"type", "EDS"},
+  Json::Object mechanism = {
+      {"clusterName", name},
+      {"max_concurrent_requests", state.update->max_concurrent_requests},
+      {"type", std::move(type)},
   };
-  if (!cluster_data.eds_service_name.empty()) {
-    discovery_mechanism["edsServiceName"] = cluster_data.eds_service_name;
+  if (!state.update->eds_service_name.empty()) {
+    mechanism["edsServiceName"] = state.update->eds_service_name;
   }
-  if (cluster_data.lrs_load_reporting_server_name.has_value()) {
-    discovery_mechanism["lrsLoadReportingServerName"] =
-        cluster_data.lrs_load_reporting_server_name.value();
+  if (state.update->lrs_load_reporting_server_name.has_value()) {
+    mechanism["lrsLoadReportingServerName"] =
+        state.update->lrs_load_reporting_server_name.value();
   }
-  Json::Object child_config = {
-      {"discoveryMechanisms",
-       Json::Array{
-           discovery_mechanism,
-       }},
-      {"localityPickingPolicy",
-       Json::Array{
-           Json::Object{
-               {"weighted_target_experimental",
-                Json::Object{
-                    {"targets", Json::Object()},
-                }},
-           },
-       }},
-      {"endpointPickingPolicy",
-       Json::Array{
-           Json::Object{
-               {"round_robin", Json::Object()},
-           },
-       }},
-  };
-  Json json = Json::Array{
-      Json::Object{
-          {"xds_cluster_resolver_experimental", std::move(child_config)},
-      },
-  };
+  discovery_mechanisms->emplace_back(std::move(mechanism));
+  return true;
+}
+
+void CdsLb::OnClusterChanged(const std::string& name,
+                             XdsApi::CdsUpdate cluster_data) {
   if (GRPC_TRACE_FLAG_ENABLED(grpc_cds_lb_trace)) {
-    std::string json_str = json.Dump(/*indent=*/1);
-    gpr_log(GPR_INFO, "[cdslb %p] generated config for child policy: %s", this,
-            json_str.c_str());
+    gpr_log(
+        GPR_INFO,
+        "[cdslb %p] received CDS update for cluster %s from xds client %p: %s",
+        this, name.c_str(), xds_client_.get(), cluster_data.ToString().c_str());
   }
-  RefCountedPtr<LoadBalancingPolicy::Config> config =
-      LoadBalancingPolicyRegistry::ParseLoadBalancingConfig(json, &error);
+  // Store the update in the map if we are still interested in watching this
+  // cluster (i.e., it is not cancelled already).
+  // If we've already deleted this entry, then this is an update notification
+  // that was scheduled before the deletion, so we can just ignore it.
+  auto it = watchers_.find(name);
+  if (it == watchers_.end()) return;
+  it->second.update = cluster_data;
+  // Take care of integration with new certificate code.
+  grpc_error_handle error = GRPC_ERROR_NONE;
+  error = UpdateXdsCertificateProvider(name, it->second.update.value());
   if (error != GRPC_ERROR_NONE) {
-    OnError(error);
-    return;
+    return OnError(name, error);
   }
-  // Create child policy if not already present.
-  if (child_policy_ == nullptr) {
-    LoadBalancingPolicy::Args args;
-    args.work_serializer = work_serializer();
-    args.args = args_;
-    args.channel_control_helper = absl::make_unique<Helper>(Ref());
-    child_policy_ = LoadBalancingPolicyRegistry::CreateLoadBalancingPolicy(
-        config->name(), std::move(args));
-    if (child_policy_ == nullptr) {
-      OnError(GRPC_ERROR_CREATE_FROM_STATIC_STRING(
-          "failed to create child policy"));
-      return;
+  // Scan the map starting from the root cluster to generate the list of
+  // discovery mechanisms. If we don't have some of the data we need (i.e., we
+  // just started up and not all watchers have returned data yet), then don't
+  // update the child policy at all.
+  Json::Array discovery_mechanisms;
+  std::set<std::string> clusters_needed;
+  if (GenerateDiscoveryMechanismForCluster(
+          config_->cluster(), &discovery_mechanisms, &clusters_needed)) {
+    // Construct config for child policy.
+    Json::Object xds_lb_policy;
+    if (cluster_data.lb_policy == "RING_HASH") {
+      std::string hash_function;
+      switch (cluster_data.hash_function) {
+        case XdsApi::CdsUpdate::HashFunction::XX_HASH:
+          hash_function = "XX_HASH";
+          break;
+        case XdsApi::CdsUpdate::HashFunction::MURMUR_HASH_2:
+          hash_function = "MURMUR_HASH_2";
+          break;
+        default:
+          GPR_ASSERT(0);
+          break;
+      }
+      xds_lb_policy["RING_HASH"] = Json::Object{
+          {"min_ring_size", cluster_data.min_ring_size},
+          {"max_ring_size", cluster_data.max_ring_size},
+          {"hash_function", hash_function},
+      };
+    } else {
+      xds_lb_policy["ROUND_ROBIN"] = Json::Object();
     }
-    grpc_pollset_set_add_pollset_set(child_policy_->interested_parties(),
-                                     interested_parties());
+    Json::Object child_config = {
+        {"xdsLbPolicy",
+         Json::Array{
+             xds_lb_policy,
+         }},
+        {"discoveryMechanisms", std::move(discovery_mechanisms)},
+    };
+    Json json = Json::Array{
+        Json::Object{
+            {"xds_cluster_resolver_experimental", std::move(child_config)},
+        },
+    };
     if (GRPC_TRACE_FLAG_ENABLED(grpc_cds_lb_trace)) {
-      gpr_log(GPR_INFO, "[cdslb %p] created child policy %s (%p)", this,
-              config->name(), child_policy_.get());
+      std::string json_str = json.Dump(/*indent=*/1);
+      gpr_log(GPR_INFO, "[cdslb %p] generated config for child policy: %s",
+              this, json_str.c_str());
     }
+    RefCountedPtr<LoadBalancingPolicy::Config> config =
+        LoadBalancingPolicyRegistry::ParseLoadBalancingConfig(json, &error);
+    if (error != GRPC_ERROR_NONE) {
+      OnError(name, error);
+      return;
+    }
+    // Create child policy if not already present.
+    if (child_policy_ == nullptr) {
+      LoadBalancingPolicy::Args args;
+      args.work_serializer = work_serializer();
+      args.args = args_;
+      args.channel_control_helper = absl::make_unique<Helper>(Ref());
+      child_policy_ = LoadBalancingPolicyRegistry::CreateLoadBalancingPolicy(
+          config->name(), std::move(args));
+      if (child_policy_ == nullptr) {
+        OnError(name, GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+                          "failed to create child policy"));
+        return;
+      }
+      grpc_pollset_set_add_pollset_set(child_policy_->interested_parties(),
+                                       interested_parties());
+      if (GRPC_TRACE_FLAG_ENABLED(grpc_cds_lb_trace)) {
+        gpr_log(GPR_INFO, "[cdslb %p] created child policy %s (%p)", this,
+                config->name(), child_policy_.get());
+      }
+    }
+    // Update child policy.
+    UpdateArgs args;
+    args.config = std::move(config);
+    if (xds_certificate_provider_ != nullptr) {
+      grpc_arg arg_to_add = xds_certificate_provider_->MakeChannelArg();
+      args.args = grpc_channel_args_copy_and_add(args_, &arg_to_add, 1);
+    } else {
+      args.args = grpc_channel_args_copy(args_);
+    }
+    child_policy_->UpdateLocked(std::move(args));
   }
-  // Update child policy.
-  UpdateArgs args;
-  args.config = std::move(config);
-  if (xds_certificate_provider_ != nullptr) {
-    grpc_arg arg_to_add = xds_certificate_provider_->MakeChannelArg();
-    args.args = grpc_channel_args_copy_and_add(args_, &arg_to_add, 1);
-  } else {
-    args.args = grpc_channel_args_copy(args_);
+  // Remove entries in watchers_ for any clusters not in clusters_needed
+  for (auto it = watchers_.begin(); it != watchers_.end();) {
+    const std::string& cluster_name = it->first;
+    if (clusters_needed.find(cluster_name) != clusters_needed.end()) {
+      ++it;
+      continue;
+    }
+    if (GRPC_TRACE_FLAG_ENABLED(grpc_cds_lb_trace)) {
+      gpr_log(GPR_INFO, "[cdslb %p] cancelling watch for cluster %s", this,
+              cluster_name.c_str());
+    }
+    CancelClusterDataWatch(cluster_name, it->second.watcher,
+                           /*delay_unsubscription=*/false);
+    it = watchers_.erase(it);
   }
-  child_policy_->UpdateLocked(std::move(args));
 }
 
-void CdsLb::OnError(grpc_error* error) {
+void CdsLb::OnError(const std::string& name, grpc_error_handle error) {
   gpr_log(GPR_ERROR, "[cdslb %p] xds error obtaining data for cluster %s: %s",
-          this, config_->cluster().c_str(), grpc_error_string(error));
+          this, name.c_str(), grpc_error_std_string(error).c_str());
   // Go into TRANSIENT_FAILURE if we have not yet created the child
   // policy (i.e., we have not yet received data from xds).  Otherwise,
   // we keep running with the data we had previously.
@@ -426,12 +558,12 @@ void CdsLb::OnError(grpc_error* error) {
   }
 }
 
-void CdsLb::OnResourceDoesNotExist() {
+void CdsLb::OnResourceDoesNotExist(const std::string& name) {
   gpr_log(GPR_ERROR,
           "[cdslb %p] CDS resource for %s does not exist -- reporting "
           "TRANSIENT_FAILURE",
-          this, config_->cluster().c_str());
-  grpc_error* error =
+          this, name.c_str());
+  grpc_error_handle error =
       grpc_error_set_int(GRPC_ERROR_CREATE_FROM_COPIED_STRING(
                              absl::StrCat("CDS resource \"", config_->cluster(),
                                           "\" does not exist")
@@ -443,8 +575,8 @@ void CdsLb::OnResourceDoesNotExist() {
   MaybeDestroyChildPolicyLocked();
 }
 
-grpc_error* CdsLb::UpdateXdsCertificateProvider(
-    const XdsApi::CdsUpdate& cluster_data) {
+grpc_error_handle CdsLb::UpdateXdsCertificateProvider(
+    const std::string& cluster_name, const XdsApi::CdsUpdate& cluster_data) {
   // Early out if channel is not configured to use xds security.
   grpc_channel_credentials* channel_credentials =
       grpc_channel_credentials_find_in_args(args_);
@@ -453,28 +585,28 @@ grpc_error* CdsLb::UpdateXdsCertificateProvider(
     xds_certificate_provider_ = nullptr;
     return GRPC_ERROR_NONE;
   }
+  if (xds_certificate_provider_ == nullptr) {
+    xds_certificate_provider_ = MakeRefCounted<XdsCertificateProvider>();
+  }
+  // Configure root cert.
   absl::string_view root_provider_instance_name =
       cluster_data.common_tls_context.combined_validation_context
           .validation_context_certificate_provider_instance.instance_name;
   absl::string_view root_provider_cert_name =
       cluster_data.common_tls_context.combined_validation_context
           .validation_context_certificate_provider_instance.certificate_name;
-  absl::string_view identity_provider_instance_name =
-      cluster_data.common_tls_context
-          .tls_certificate_certificate_provider_instance.instance_name;
-  absl::string_view identity_provider_cert_name =
-      cluster_data.common_tls_context
-          .tls_certificate_certificate_provider_instance.certificate_name;
   RefCountedPtr<XdsCertificateProvider> new_root_provider;
   if (!root_provider_instance_name.empty()) {
     new_root_provider =
         xds_client_->certificate_provider_store()
             .CreateOrGetCertificateProvider(root_provider_instance_name);
     if (new_root_provider == nullptr) {
-      return GRPC_ERROR_CREATE_FROM_COPIED_STRING(
-          absl::StrCat("Certificate provider instance name: \"",
-                       root_provider_instance_name, "\" not recognized.")
-              .c_str());
+      return grpc_error_set_int(
+          GRPC_ERROR_CREATE_FROM_COPIED_STRING(
+              absl::StrCat("Certificate provider instance name: \"",
+                           root_provider_instance_name, "\" not recognized.")
+                  .c_str()),
+          GRPC_ERROR_INT_GRPC_STATUS, GRPC_STATUS_UNAVAILABLE);
     }
   }
   if (root_certificate_provider_ != new_root_provider) {
@@ -491,16 +623,31 @@ grpc_error* CdsLb::UpdateXdsCertificateProvider(
     }
     root_certificate_provider_ = std::move(new_root_provider);
   }
+  xds_certificate_provider_->UpdateRootCertNameAndDistributor(
+      cluster_name, root_provider_cert_name,
+      root_certificate_provider_ == nullptr
+          ? nullptr
+          : root_certificate_provider_->distributor());
+  // Configure identity cert.
+  absl::string_view identity_provider_instance_name =
+      cluster_data.common_tls_context
+          .tls_certificate_certificate_provider_instance.instance_name;
+  absl::string_view identity_provider_cert_name =
+      cluster_data.common_tls_context
+          .tls_certificate_certificate_provider_instance.certificate_name;
   RefCountedPtr<XdsCertificateProvider> new_identity_provider;
   if (!identity_provider_instance_name.empty()) {
     new_identity_provider =
         xds_client_->certificate_provider_store()
             .CreateOrGetCertificateProvider(identity_provider_instance_name);
     if (new_identity_provider == nullptr) {
-      return GRPC_ERROR_CREATE_FROM_COPIED_STRING(
-          absl::StrCat("Certificate provider instance name: \"",
-                       identity_provider_instance_name, "\" not recognized.")
-              .c_str());
+      return grpc_error_set_int(
+          GRPC_ERROR_CREATE_FROM_COPIED_STRING(
+              absl::StrCat("Certificate provider instance name: \"",
+                           identity_provider_instance_name,
+                           "\" not recognized.")
+                  .c_str()),
+          GRPC_ERROR_INT_GRPC_STATUS, GRPC_STATUS_UNAVAILABLE);
     }
   }
   if (identity_certificate_provider_ != new_identity_provider) {
@@ -517,56 +664,34 @@ grpc_error* CdsLb::UpdateXdsCertificateProvider(
     }
     identity_certificate_provider_ = std::move(new_identity_provider);
   }
-  const std::vector<XdsApi::StringMatcher>& match_subject_alt_names =
+  xds_certificate_provider_->UpdateIdentityCertNameAndDistributor(
+      cluster_name, identity_provider_cert_name,
+      identity_certificate_provider_ == nullptr
+          ? nullptr
+          : identity_certificate_provider_->distributor());
+  // Configure SAN matchers.
+  const std::vector<StringMatcher>& match_subject_alt_names =
       cluster_data.common_tls_context.combined_validation_context
           .default_validation_context.match_subject_alt_names;
-  if (!root_provider_instance_name.empty() &&
-      !identity_provider_instance_name.empty()) {
-    // Using mTLS configuration
-    if (xds_certificate_provider_ != nullptr &&
-        xds_certificate_provider_->ProvidesRootCerts() &&
-        xds_certificate_provider_->ProvidesIdentityCerts()) {
-      xds_certificate_provider_->UpdateRootCertNameAndDistributor(
-          root_provider_cert_name, root_certificate_provider_->distributor());
-      xds_certificate_provider_->UpdateIdentityCertNameAndDistributor(
-          identity_provider_cert_name,
-          identity_certificate_provider_->distributor());
-      xds_certificate_provider_->UpdateSubjectAlternativeNameMatchers(
-          match_subject_alt_names);
-    } else {
-      // Existing xDS certificate provider does not have mTLS configuration.
-      // Create new certificate provider so that new subchannel connectors are
-      // created.
-      xds_certificate_provider_ = MakeRefCounted<XdsCertificateProvider>(
-          root_provider_cert_name, root_certificate_provider_->distributor(),
-          identity_provider_cert_name,
-          identity_certificate_provider_->distributor(),
-          match_subject_alt_names);
-    }
-  } else if (!root_provider_instance_name.empty()) {
-    // Using TLS configuration
-    if (xds_certificate_provider_ != nullptr &&
-        xds_certificate_provider_->ProvidesRootCerts() &&
-        !xds_certificate_provider_->ProvidesIdentityCerts()) {
-      xds_certificate_provider_->UpdateRootCertNameAndDistributor(
-          root_provider_cert_name, root_certificate_provider_->distributor());
-      xds_certificate_provider_->UpdateSubjectAlternativeNameMatchers(
-          match_subject_alt_names);
-    } else {
-      // Existing xDS certificate provider does not have TLS configuration.
-      // Create new certificate provider so that new subchannel connectors are
-      // created.
-      xds_certificate_provider_ = MakeRefCounted<XdsCertificateProvider>(
-          root_provider_cert_name, root_certificate_provider_->distributor(),
-          "", nullptr, match_subject_alt_names);
-    }
-  } else {
-    // No configuration provided.
-    xds_certificate_provider_ = nullptr;
-  }
+  xds_certificate_provider_->UpdateSubjectAlternativeNameMatchers(
+      cluster_name, match_subject_alt_names);
   return GRPC_ERROR_NONE;
 }
 
+void CdsLb::CancelClusterDataWatch(absl::string_view cluster_name,
+                                   XdsClient::ClusterWatcherInterface* watcher,
+                                   bool delay_unsubscription) {
+  if (xds_certificate_provider_ != nullptr) {
+    std::string name(cluster_name);
+    xds_certificate_provider_->UpdateRootCertNameAndDistributor(name, "",
+                                                                nullptr);
+    xds_certificate_provider_->UpdateIdentityCertNameAndDistributor(name, "",
+                                                                    nullptr);
+    xds_certificate_provider_->UpdateSubjectAlternativeNameMatchers(name, {});
+  }
+  xds_client_->CancelClusterDataWatch(cluster_name, watcher,
+                                      delay_unsubscription);
+}
 //
 // factory
 //
@@ -575,13 +700,12 @@ class CdsLbFactory : public LoadBalancingPolicyFactory {
  public:
   OrphanablePtr<LoadBalancingPolicy> CreateLoadBalancingPolicy(
       LoadBalancingPolicy::Args args) const override {
-    grpc_error* error = GRPC_ERROR_NONE;
-    RefCountedPtr<XdsClient> xds_client = XdsClient::GetOrCreate(&error);
-    if (error != GRPC_ERROR_NONE) {
+    RefCountedPtr<XdsClient> xds_client =
+        XdsClient::GetFromChannelArgs(*args.args);
+    if (xds_client == nullptr) {
       gpr_log(GPR_ERROR,
-              "cannot get XdsClient to instantiate cds LB policy: %s",
-              grpc_error_string(error));
-      GRPC_ERROR_UNREF(error);
+              "XdsClient not present in channel args -- cannot instantiate "
+              "cds LB policy");
       return nullptr;
     }
     return MakeOrphanable<CdsLb>(std::move(xds_client), std::move(args));
@@ -590,7 +714,7 @@ class CdsLbFactory : public LoadBalancingPolicyFactory {
   const char* name() const override { return kCds; }
 
   RefCountedPtr<LoadBalancingPolicy::Config> ParseLoadBalancingConfig(
-      const Json& json, grpc_error** error) const override {
+      const Json& json, grpc_error_handle* error) const override {
     GPR_DEBUG_ASSERT(error != nullptr && *error == GRPC_ERROR_NONE);
     if (json.type() == Json::Type::JSON_NULL) {
       // xds was mentioned as a policy in the deprecated loadBalancingPolicy
@@ -600,7 +724,8 @@ class CdsLbFactory : public LoadBalancingPolicyFactory {
           "Please use loadBalancingConfig field of service config instead.");
       return nullptr;
     }
-    std::vector<grpc_error*> error_list;
+    std::vector<grpc_error_handle> error_list;
+    // cluster name.
     std::string cluster;
     auto it = json.object_value().find("cluster");
     if (it == json.object_value().end()) {