Support gRPC health checking

This addresses flyteorg/flyte#489.

For now only server level health checking is supported but we could
extend to service level when needed later.

cmd/entrypoints/serve.go

@@ -11,6 +11,8 @@ import (
 	"github.com/lyft/flytestdlib/logger"
 	"github.com/spf13/cobra"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/health"
+	"google.golang.org/grpc/health/grpc_health_v1"
 	"google.golang.org/grpc/reflection"
 )
 
@@ -54,6 +56,11 @@ func serveInsecure(ctx context.Context, cfg *config.Config) error {
 func newGRPCServer(_ context.Context, cfg *config.Config) *grpc.Server {
 	grpcServer := grpc.NewServer()
 	datacatalog.RegisterDataCatalogServer(grpcServer, datacatalogservice.NewDataCatalogService())
+
+	healthServer := health.NewServer()
+	healthServer.SetServingStatus("", grpc_health_v1.HealthCheckResponse_SERVING)
+	grpc_health_v1.RegisterHealthServer(grpcServer, healthServer)
+
 	if cfg.GrpcServerReflection {
 		reflection.Register(grpcServer)
 	}