configuring load balancing per ingress (#2167)

* configure load balancing through a ingress annotation

* update docs

internal/ingress/controller/controller.go

@@ -599,6 +599,9 @@ func (n *NGINXController) createUpstreams(data []*extensions.Ingress, du *ingres
 			if upstreams[defBackend].UpstreamHashBy == "" {
 				upstreams[defBackend].UpstreamHashBy = anns.UpstreamHashBy
 			}
+			if upstreams[defBackend].LoadBalancing == "" {
+				upstreams[defBackend].LoadBalancing = anns.LoadBalancing
+			}
 
 			svcKey := fmt.Sprintf("%v/%v", ing.GetNamespace(), ing.Spec.Backend.ServiceName)
 
@@ -654,6 +657,10 @@ func (n *NGINXController) createUpstreams(data []*extensions.Ingress, du *ingres
 					upstreams[name].UpstreamHashBy = anns.UpstreamHashBy
 				}
 
+				if upstreams[name].LoadBalancing == "" {
+					upstreams[name].LoadBalancing = anns.LoadBalancing
+				}
+
 				svcKey := fmt.Sprintf("%v/%v", ing.GetNamespace(), path.Backend.ServiceName)
 
 				// Add the service cluster endpoint as the upstream instead of individual endpoints

internal/ingress/controller/template/template.go

@@ -122,6 +122,7 @@ var (
 		"buildLocation":            buildLocation,
 		"buildAuthLocation":        buildAuthLocation,
 		"buildAuthResponseHeaders": buildAuthResponseHeaders,
+		"buildLoadBalancingConfig": buildLoadBalancingConfig,
 		"buildProxyPass":           buildProxyPass,
 		"filterRateLimits":         filterRateLimits,
 		"buildRateLimitZones":      buildRateLimitZones,
@@ -277,6 +278,31 @@ func buildLogFormatUpstream(input interface{}) string {
 	return cfg.BuildLogFormatUpstream()
 }
 
+func buildLoadBalancingConfig(b interface{}, fallbackLoadBalancing string) string {
+	backend, ok := b.(*ingress.Backend)
+	if !ok {
+		glog.Errorf("expected an '*ingress.Backend' type but %T was returned", b)
+		return ""
+	}
+
+	if backend.UpstreamHashBy != "" {
+		return "hash {{ $upstream.UpstreamHashBy }} consistent;"
+	}
+
+	if backend.LoadBalancing != "" {
+		if backend.LoadBalancing == "round_robin" {
+			return ""
+		}
+		return fmt.Sprintf("%s;", backend.LoadBalancing)
+	}
+
+	if fallbackLoadBalancing == "round_robin" {
+		return ""
+	}
+
+	return fmt.Sprintf("%s;", fallbackLoadBalancing)
+}
+
 // buildProxyPass produces the proxy pass string, if the ingress has redirects
 // (specified through the nginx.ingress.kubernetes.io/rewrite-to annotation)
 // If the annotation nginx.ingress.kubernetes.io/add-base-url:"true" is specified it will