BAARC-98: Implement grpc health checking protocol https://github.com/…

…grpc/grpc/blob/master/doc/health-checking.md

Makefile

@@ -60,6 +60,14 @@ gen:
 	--go-grpc_opt=paths=source_relative \
 	metamorph/metamorph_api/metamorph_api.proto
 
+	protoc \
+	--proto_path=. \
+	--go_out=. \
+	--go_opt=paths=source_relative \
+	--go-grpc_out=. \
+	--go-grpc_opt=paths=source_relative \
+	metamorph/health/grpc_health_check.proto
+
 	protoc \
 	--proto_path=. \
 	--go_out=. \

metamorph/health/grpc_health_check.proto

@@ -0,0 +1,25 @@
+syntax = "proto3";
+
+option go_package = ".;healthcheck";
+
+package grpc.health.v1;
+
+message HealthCheckRequest {
+  string service = 1;
+}
+
+message HealthCheckResponse {
+  enum ServingStatus {
+    UNKNOWN = 0;
+    SERVING = 1;
+    NOT_SERVING = 2;
+    SERVICE_UNKNOWN = 3;  // Used only by the Watch method.
+  }
+  ServingStatus status = 1;
+}
+
+service Health {
+  rpc Check(HealthCheckRequest) returns (HealthCheckResponse);
+
+  rpc Watch(HealthCheckRequest) returns (stream HealthCheckResponse);
+}