[thrift_proxy] Add and implement weighted clusters to thrift.RouteAction (#4315)

Adding the ability to add weighted clusters to the thrift router's RouteAction proto. This works much like the http one and borrows a great deal of code from it. Since the thrift_proxy Route and RouteEntry interfaces are much more bare bones, was able to implement the WeightedClusterEntry class.

Risk Level: Low
Testing: Tests, new and old, pass
Doc Changes: inline
Release Notes: n/a

Signed-off-by: Brian Ramos <brirams@users.noreply.github.com>

Mirrored from https://github.com/envoyproxy/envoy @ a50ac3747623a7fa74a5dbd33eacf0808dbf4d0c

envoy/config/filter/network/thrift_proxy/v2alpha1/BUILD

@@ -9,6 +9,7 @@ api_proto_library_internal(
         "thrift_proxy.proto",
     ],
     deps = [
+        "//envoy/api/v2/core:base",
         "//envoy/api/v2/route",
     ],
 )

envoy/config/filter/network/thrift_proxy/v2alpha1/route.proto

@@ -3,7 +3,11 @@ syntax = "proto3";
 package envoy.config.filter.network.thrift_proxy.v2alpha1;
 option go_package = "v2";
 
+import "envoy/api/v2/core/base.proto";
 import "envoy/api/v2/route/route.proto";
+
+import "google/protobuf/wrappers.proto";
+
 import "validate/validate.proto";
 import "gogoproto/gogo.proto";
 
@@ -66,8 +70,36 @@ message RouteMatch {
   repeated envoy.api.v2.route.HeaderMatcher headers = 4;
 }
 
-// [#comment:next free field: 2]
+// [#comment:next free field: 3]
 message RouteAction {
-  // Indicates the upstream cluster to which the request should be routed.
-  string cluster = 1 [(validate.rules).string.min_bytes = 1];
+  oneof cluster_specifier {
+    option (validate.required) = true;
+
+    // Indicates a single upstream cluster to which the request should be routed
+    // to.
+    string cluster = 1 [(validate.rules).string.min_bytes = 1];
+
+    // Multiple upstream clusters can be specified for a given route. The
+    // request is routed to one of the upstream clusters based on weights
+    // assigned to each cluster.
+    WeightedCluster weighted_clusters = 2;
+  }
+}
+
+// Allows for specification of multiple upstream clusters along with weights that indicate the
+// percentage of traffic to be forwarded to each cluster. The router selects an upstream cluster
+// based on these weights.
+message WeightedCluster {
+  message ClusterWeight {
+    // Name of the upstream cluster.
+    string name = 1 [(validate.rules).string.min_bytes = 1];
+
+    // When a request matches the route, the choice of an upstream cluster is determined by its
+    // weight. The sum of weights across all entries in the clusters array determines the total
+    // weight.
+    google.protobuf.UInt32Value weight = 2 [(validate.rules).uint32.gte = 1];
+  }
+
+  // Specifies one or more upstream clusters associated with the route.
+  repeated ClusterWeight clusters = 1 [(validate.rules).repeated .min_items = 1];
 }