diff --git a/include/envoy/config/grpc_mux.h b/include/envoy/config/grpc_mux.h
index c07b0bab16464..41af0fd2e60eb 100644
--- a/include/envoy/config/grpc_mux.h
+++ b/include/envoy/config/grpc_mux.h
@@ -73,6 +73,14 @@ class GrpcMux {
                                   const std::set<std::string>& resources,
                                   SubscriptionCallbacks& callbacks,
                                   std::chrono::milliseconds init_fetch_timeout) PURE;
+  /**
+   * The only difference between addToWatch() and addOrUpdateWatch() is that the 'resources' here
+   * means the *extra* resources we interested in.
+   */
+  virtual Watch* addToWatch(const std::string& type_url, Watch* watch,
+                            const std::set<std::string>& resources,
+                            SubscriptionCallbacks& callbacks,
+                            std::chrono::milliseconds init_fetch_timeout) PURE;
 
   /**
    * Cleanup of a Watch* added by addOrUpdateWatch(). Receiving a Watch* from addOrUpdateWatch()
diff --git a/include/envoy/config/subscription.h b/include/envoy/config/subscription.h
index 009c4a265dc6c..0f6a14dbf3467 100644
--- a/include/envoy/config/subscription.h
+++ b/include/envoy/config/subscription.h
@@ -90,6 +90,12 @@ class Subscription {
    * be passed to std::set_difference, which must be given sorted collections.
    */
   virtual void updateResourceInterest(const std::set<std::string>& update_to_these_names) PURE;
+
+  /**
+   * Add the resources to fetch.
+   * @param resources vector of resource names to fetch.
+   */
+  virtual void addToResourceInterest(const std::set<std::string>&){};
 };
 
 using SubscriptionPtr = std::unique_ptr<Subscription>;
diff --git a/include/envoy/upstream/cluster_manager.h b/include/envoy/upstream/cluster_manager.h
index 8974edf4cd080..9641569b6390c 100644
--- a/include/envoy/upstream/cluster_manager.h
+++ b/include/envoy/upstream/cluster_manager.h
@@ -224,6 +224,10 @@ class ClusterManager {
    * @return Config::SubscriptionFactory& the subscription factory.
    */
   virtual Config::SubscriptionFactory& subscriptionFactory() PURE;
+
+  virtual void updateClusterInterest(const std::set<std::string>& update_to_these_names) PURE;
+
+  virtual void addToClusterInterest(const std::set<std::string>& add_these_names) PURE;
 };
 
 using ClusterManagerPtr = std::unique_ptr<ClusterManager>;
@@ -250,6 +254,16 @@ class CdsApi {
    * @return std::string last accepted version from fetch.
    */
   virtual const std::string versionInfo() const PURE;
+
+  /**
+   * Update watch set of cluster resources interested.
+   */
+  virtual void updateClusterInterest(const std::set<std::string>& update_to_these_names) PURE;
+
+  /**
+   * Add watch set of cluster resources interested.
+   */
+  virtual void addToClusterInterest(const std::set<std::string>& add_these_names) PURE;
 };
 
 using CdsApiPtr = std::unique_ptr<CdsApi>;
diff --git a/source/common/config/grpc_mux_impl.cc b/source/common/config/grpc_mux_impl.cc
index 93662e0e21c49..586f832a820bc 100644
--- a/source/common/config/grpc_mux_impl.cc
+++ b/source/common/config/grpc_mux_impl.cc
@@ -22,11 +22,24 @@ Watch* GrpcMuxImpl::addOrUpdateWatch(const std::string& type_url, Watch* watch,
                                      SubscriptionCallbacks& callbacks,
                                      std::chrono::milliseconds init_fetch_timeout) {
   if (watch == nullptr) {
-    return addWatch(type_url, resources, callbacks, init_fetch_timeout);
-  } else {
-    updateWatch(type_url, watch, resources);
-    return watch;
+    watch = addWatch(type_url, callbacks, init_fetch_timeout);
   }
+  // updateWatch() queues a discovery request if any of 'resources' are not yet subscribed.
+  updateWatch(type_url, watch, resources);
+  return watch;
+}
+
+Watch* GrpcMuxImpl::addToWatch(const std::string& type_url, Watch* watch,
+                               const std::set<std::string>& resources,
+                               SubscriptionCallbacks& callbacks,
+                               std::chrono::milliseconds init_fetch_timeout) {
+  if (watch == nullptr) {
+    watch = addWatch(type_url, callbacks, init_fetch_timeout);
+  }
+  // addToWatch() queues a discovery request for any of *extra* 'resources' we are not yet
+  // subscribed.
+  addToWatch(type_url, watch, resources);
+  return watch;
 }
 
 void GrpcMuxImpl::removeWatch(const std::string& type_url, Watch* watch) {
@@ -95,8 +108,7 @@ void GrpcMuxImpl::handleStreamEstablishmentFailure() {
   } while (all_subscribed.size() != subscriptions_.size());
 }
 
-Watch* GrpcMuxImpl::addWatch(const std::string& type_url, const std::set<std::string>& resources,
-                             SubscriptionCallbacks& callbacks,
+Watch* GrpcMuxImpl::addWatch(const std::string& type_url, SubscriptionCallbacks& callbacks,
                              std::chrono::milliseconds init_fetch_timeout) {
   auto watch_map = watch_maps_.find(type_url);
   if (watch_map == watch_maps_.end()) {
@@ -108,11 +120,24 @@ Watch* GrpcMuxImpl::addWatch(const std::string& type_url, const std::set<std::st
   }
 
   Watch* watch = watch_map->second->addWatch(callbacks);
-  // updateWatch() queues a discovery request if any of 'resources' are not yet subscribed.
-  updateWatch(type_url, watch, resources);
   return watch;
 }
 
+void GrpcMuxImpl::addToWatch(const std::string& type_url, Watch* watch,
+                             const std::set<std::string>& resources) {
+  ASSERT(watch != nullptr);
+  SubscriptionState& sub = subscriptionStateFor(type_url);
+  WatchMap& watch_map = watchMapFor(type_url);
+
+  auto added_removed = watch_map.addToWatchInterest(watch, resources);
+  sub.updateSubscriptionInterest(added_removed.added_, added_removed.removed_);
+
+  // Tell the server about our change in interest, if any.
+  if (sub.subscriptionUpdatePending()) {
+    trySendDiscoveryRequests();
+  }
+}
+
 // Updates the list of resource names watched by the given watch. If an added name is new across
 // the whole subscription, or if a removed name has no other watch interested in it, then the
 // subscription will enqueue and attempt to send an appropriate discovery request.
diff --git a/source/common/config/grpc_mux_impl.h b/source/common/config/grpc_mux_impl.h
index ff0d5db75e89e..2ef06369ec878 100644
--- a/source/common/config/grpc_mux_impl.h
+++ b/source/common/config/grpc_mux_impl.h
@@ -29,6 +29,11 @@ class GrpcMuxImpl : public GrpcMux, Logger::Loggable<Logger::Id::config> {
   Watch* addOrUpdateWatch(const std::string& type_url, Watch* watch,
                           const std::set<std::string>& resources, SubscriptionCallbacks& callbacks,
                           std::chrono::milliseconds init_fetch_timeout) override;
+
+  Watch* addToWatch(const std::string& type_url, Watch* watch,
+                    const std::set<std::string>& resources, SubscriptionCallbacks& callbacks,
+                    std::chrono::milliseconds init_fetch_timeout) override;
+
   void removeWatch(const std::string& type_url, Watch* watch) override;
 
   void pause(const std::string& type_url) override;
@@ -67,8 +72,11 @@ class GrpcMuxImpl : public GrpcMux, Logger::Loggable<Logger::Id::config> {
   const LocalInfo::LocalInfo& local_info() const { return local_info_; }
 
 private:
-  Watch* addWatch(const std::string& type_url, const std::set<std::string>& resources,
-                  SubscriptionCallbacks& callbacks, std::chrono::milliseconds init_fetch_timeout);
+  Watch* addWatch(const std::string& type_url, SubscriptionCallbacks& callbacks,
+                  std::chrono::milliseconds init_fetch_timeout);
+
+  void addToWatch(const std::string& type_url, Watch* watch,
+                  const std::set<std::string>& resources);
 
   // Updates the list of resource names watched by the given watch. If an added name is new across
   // the whole subscription, or if a removed name has no other watch interested in it, then the
@@ -188,6 +196,10 @@ class NullGrpcMuxImpl : public GrpcMux {
                           SubscriptionCallbacks&, std::chrono::milliseconds) override {
     throw EnvoyException("ADS must be configured to support an ADS config source");
   }
+  Watch* addToWatch(const std::string&, Watch*, const std::set<std::string>&,
+                    SubscriptionCallbacks&, std::chrono::milliseconds) override {
+    throw EnvoyException("ADS must be configured to support an ADS config source");
+  }
   void removeWatch(const std::string&, Watch*) override {
     throw EnvoyException("ADS must be configured to support an ADS config source");
   }
diff --git a/source/common/config/grpc_subscription_impl.cc b/source/common/config/grpc_subscription_impl.cc
index 77f003b061b57..730b6264977e9 100644
--- a/source/common/config/grpc_subscription_impl.cc
+++ b/source/common/config/grpc_subscription_impl.cc
@@ -39,6 +39,11 @@ void GrpcSubscriptionImpl::updateResourceInterest(
   stats_.update_attempt_.inc();
 }
 
+void GrpcSubscriptionImpl::addToResourceInterest(const std::set<std::string>& add_these_names) {
+  watch_ = grpc_mux_->addToWatch(type_url_, watch_, add_these_names, *this, init_fetch_timeout_);
+  stats_.update_attempt_.inc();
+}
+
 // Config::SubscriptionCallbacks
 void GrpcSubscriptionImpl::onConfigUpdate(
     const Protobuf::RepeatedPtrField<ProtobufWkt::Any>& resources,
diff --git a/source/common/config/grpc_subscription_impl.h b/source/common/config/grpc_subscription_impl.h
index 46968aa3d71b1..e2889e12c0a60 100644
--- a/source/common/config/grpc_subscription_impl.h
+++ b/source/common/config/grpc_subscription_impl.h
@@ -41,6 +41,7 @@ class GrpcSubscriptionImpl : public Subscription, public SubscriptionCallbacks {
   // Config::Subscription
   void start(const std::set<std::string>& resource_names) override;
   void updateResourceInterest(const std::set<std::string>& update_to_these_names) override;
+  void addToResourceInterest(const std::set<std::string>& add_these_names) override;
 
   // Config::SubscriptionCallbacks (all pass through to callbacks_!)
   void onConfigUpdate(const Protobuf::RepeatedPtrField<ProtobufWkt::Any>& resources,
diff --git a/source/common/config/watch_map.cc b/source/common/config/watch_map.cc
index adc99f145f559..6b85d89b7ce4a 100644
--- a/source/common/config/watch_map.cc
+++ b/source/common/config/watch_map.cc
@@ -40,6 +40,17 @@ AddedRemoved WatchMap::updateWatchInterest(Watch* watch,
                       findRemovals(newly_removed_from_watch, watch));
 }
 
+AddedRemoved WatchMap::addToWatchInterest(Watch* watch,
+                                          const std::set<std::string>& add_these_names) {
+  std::vector<std::string> newly_added_to_watch(add_these_names.begin(), add_these_names.end());
+  std::vector<std::string> newly_removed_from_watch;
+  watch->resource_names_.insert(add_these_names.begin(), add_these_names.end());
+  std::set<std::string> additions = add_these_names;
+
+  return AddedRemoved(findAdditions(newly_added_to_watch, watch),
+                      findRemovals(newly_removed_from_watch, watch));
+}
+
 absl::flat_hash_set<Watch*> WatchMap::watchesInterestedIn(const std::string& resource_name) {
   absl::flat_hash_set<Watch*> ret = wildcard_watches_;
   const auto watches_interested = watch_interest_.find(resource_name);
diff --git a/source/common/config/watch_map.h b/source/common/config/watch_map.h
index e98c8af171221..8f8e7644a7786 100644
--- a/source/common/config/watch_map.h
+++ b/source/common/config/watch_map.h
@@ -70,6 +70,8 @@ class WatchMap : public SubscriptionCallbacks, public Logger::Loggable<Logger::I
   //    Y will be in removed_.
   AddedRemoved updateWatchInterest(Watch* watch,
                                    const std::set<std::string>& update_to_these_names);
+  // Adds the extra set of resource names that the given watch should watch.
+  AddedRemoved addToWatchInterest(Watch* watch, const std::set<std::string>& add_these_names);
 
   // Expects that the watch to be removed has already had all of its resource names removed via
   // updateWatchInterest().
diff --git a/source/common/upstream/cds_api_impl.h b/source/common/upstream/cds_api_impl.h
index b17d4bbc9989d..03161eaf6fdb4 100644
--- a/source/common/upstream/cds_api_impl.h
+++ b/source/common/upstream/cds_api_impl.h
@@ -33,6 +33,14 @@ class CdsApiImpl : public CdsApi,
   }
   const std::string versionInfo() const override { return system_version_info_; }
 
+  void updateClusterInterest(const std::set<std::string>& update_to_these_names) override {
+    subscription_->updateResourceInterest(update_to_these_names);
+  }
+
+  void addToClusterInterest(const std::set<std::string>& add_these_names) override {
+    subscription_->addToResourceInterest(add_these_names);
+  }
+
 private:
   // Config::SubscriptionCallbacks
   void onConfigUpdate(const Protobuf::RepeatedPtrField<ProtobufWkt::Any>& resources,
diff --git a/source/common/upstream/cluster_manager_impl.h b/source/common/upstream/cluster_manager_impl.h
index 4740267a29d39..595ce0286a47a 100644
--- a/source/common/upstream/cluster_manager_impl.h
+++ b/source/common/upstream/cluster_manager_impl.h
@@ -238,6 +238,14 @@ class ClusterManagerImpl : public ClusterManager, Logger::Loggable<Logger::Id::u
 
   Config::SubscriptionFactory& subscriptionFactory() override { return subscription_factory_; }
 
+  void updateClusterInterest(const std::set<std::string>& update_to_these_names) override {
+    cds_api_->updateClusterInterest(update_to_these_names);
+  }
+
+  void addToClusterInterest(const std::set<std::string>& add_these_names) override {
+    cds_api_->addToClusterInterest(add_these_names);
+  }
+
 protected:
   virtual void postThreadLocalDrainConnections(const Cluster& cluster,
                                                const HostVector& hosts_removed);
diff --git a/test/common/config/delta_subscription_impl_test.cc b/test/common/config/delta_subscription_impl_test.cc
index 65777ec1217f0..6cf12ac30dea1 100644
--- a/test/common/config/delta_subscription_impl_test.cc
+++ b/test/common/config/delta_subscription_impl_test.cc
@@ -50,6 +50,12 @@ TEST_F(DeltaSubscriptionImplTest, PauseHoldsRequest) {
   subscription_->resume();
 }
 
+TEST_F(DeltaSubscriptionImplTest, AddResourceCauseRequest) {
+  startSubscription({});
+  expectSendMessage({"name1", "name2"}, {}, Grpc::Status::WellKnownGrpcStatus::Ok, "", {});
+  subscription_->addToResourceInterest({"name1", "name2"});
+}
+
 TEST_F(DeltaSubscriptionImplTest, ResponseCausesAck) {
   startSubscription({"name1"});
   deliverConfigUpdate({"name1"}, "someversion", true);
diff --git a/test/mocks/config/mocks.h b/test/mocks/config/mocks.h
index ee4bae564f761..0af6d52116cd9 100644
--- a/test/mocks/config/mocks.h
+++ b/test/mocks/config/mocks.h
@@ -72,6 +72,10 @@ class MockGrpcMux : public GrpcMux {
                Watch*(const std::string& type_url, Watch* watch,
                       const std::set<std::string>& resources, SubscriptionCallbacks& callbacks,
                       std::chrono::milliseconds init_fetch_timeout));
+  MOCK_METHOD5(addToWatch,
+               Watch*(const std::string& type_url, Watch* watch,
+                      const std::set<std::string>& resources, SubscriptionCallbacks& callbacks,
+                      std::chrono::milliseconds init_fetch_timeout));
   MOCK_METHOD2(removeWatch, void(const std::string& type_url, Watch* watch));
   MOCK_METHOD1(pause, void(const std::string& type_url));
   MOCK_METHOD1(resume, void(const std::string& type_url));
diff --git a/test/mocks/upstream/mocks.h b/test/mocks/upstream/mocks.h
index 4b7151d295d8e..981d8ec1825e7 100644
--- a/test/mocks/upstream/mocks.h
+++ b/test/mocks/upstream/mocks.h
@@ -328,6 +328,8 @@ class MockClusterManager : public ClusterManager {
   MOCK_METHOD1(addThreadLocalClusterUpdateCallbacks_,
                ClusterUpdateCallbacksHandle*(ClusterUpdateCallbacks& callbacks));
   MOCK_METHOD0(subscriptionFactory, Config::SubscriptionFactory&());
+  MOCK_METHOD1(updateClusterInterest, void(const std::set<std::string>&));
+  MOCK_METHOD1(addToClusterInterest, void(const std::set<std::string>&));
 
   NiceMock<Http::ConnectionPool::MockInstance> conn_pool_;
   NiceMock<Http::MockAsyncClient> async_client_;
@@ -382,6 +384,8 @@ class MockCdsApi : public CdsApi {
   MOCK_METHOD0(initialize, void());
   MOCK_METHOD1(setInitializedCb, void(std::function<void()> callback));
   MOCK_CONST_METHOD0(versionInfo, const std::string());
+  MOCK_METHOD1(updateClusterInterest, void(const std::set<std::string>&));
+  MOCK_METHOD1(addToClusterInterest, void(const std::set<std::string>&));
 
   std::function<void()> initialized_callback_;
 };