Reimplement fall back to default load balancing

Author: b1tamara

src/code.cloudfoundry.org/gorouter/proxy/round_tripper/proxy_round_tripper.go

@@ -137,7 +137,7 @@ func (rt *roundTripper) RoundTrip(originalRequest *http.Request) (*http.Response
 			if headerValue != "" {
 				iter.(*route.HashBased).HeaderValue = headerValue
 			} else {
-				iter = reqInfo.RoutePool.FallBackToDefaultLoadBalancing(rt.logger, stickyEndpointID, mustBeSticky, rt.config.LoadBalanceAZPreference, rt.config.Zone)
+				iter = reqInfo.RoutePool.FallBackToDefaultLoadBalancing(rt.config.LoadBalance, rt.logger, stickyEndpointID, mustBeSticky, rt.config.LoadBalanceAZPreference, rt.config.Zone)
 			}
 		}
 	}

src/code.cloudfoundry.org/gorouter/route/pool.go

@@ -491,11 +491,20 @@ func (p *EndpointPool) Endpoints(logger *slog.Logger, initial string, mustBeStic
 	}
 }
 
-func (p *EndpointPool) FallBackToDefaultLoadBalancing(logger *slog.Logger, initial string, mustBeSticky bool, azPreference string, az string) EndpointIterator {
+func (p *EndpointPool) FallBackToDefaultLoadBalancing(defaultLBAlgo string, logger *slog.Logger, initial string, mustBeSticky bool, azPreference string, az string) EndpointIterator {
 	logger.Info("hash-based-routing-header-not-found",
 		slog.String("poolLBAlgorithm", p.LoadBalancingAlgorithm),
 		slog.String("Host", p.host),
 		slog.String("Path", p.contextPath))
+
+	switch defaultLBAlgo {
+	case config.LOAD_BALANCE_LC:
+		logger.Debug("endpoint-iterator-with-least-connection-lb-algo")
+		return NewLeastConnection(logger, p, initial, mustBeSticky, azPreference == config.AZ_PREF_LOCAL, az)
+	case config.LOAD_BALANCE_RR:
+		logger.Debug("endpoint-iterator-with-round-robin-lb-algo")
+		return NewRoundRobin(logger, p, initial, mustBeSticky, azPreference == config.AZ_PREF_LOCAL, az)
+	}
 	return NewRoundRobin(logger, p, initial, mustBeSticky, azPreference == config.AZ_PREF_LOCAL, az)
 }