Consistent hashing to a subset of nodes. It works like consistent hash,

but instead of mapping to a single node, we map to a subset of nodes.

test/e2e/annotations/upstreamhashby.go

@@ -0,0 +1,106 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package annotations
+
+import (
+	"fmt"
+	"net/http"
+	"regexp"
+	"strings"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+	"github.com/parnurzeal/gorequest"
+
+	"k8s.io/apimachinery/pkg/util/wait"
+	"k8s.io/ingress-nginx/test/e2e/framework"
+)
+
+func startIngress(f *framework.Framework, annotations *map[string]string) map[string]bool {
+	host := "upstream-hash-by.foo.com"
+
+	ing := framework.NewSingleIngress(host, "/", host, f.IngressController.Namespace, "http-svc", 80, annotations)
+	f.EnsureIngress(ing)
+	f.WaitForNginxServer(host,
+		func(server string) bool {
+			return strings.Contains(server, fmt.Sprintf("server_name %s ;", host))
+		})
+
+	err := wait.PollImmediate(framework.Poll, framework.DefaultTimeout, func() (bool, error) {
+		resp, _, _ := gorequest.New().
+			Get(f.IngressController.HTTPURL).
+			Set("Host", host).
+			End()
+		if resp.StatusCode == http.StatusOK {
+			return true, nil
+		}
+		return false, nil
+	})
+	Expect(err).Should(BeNil())
+
+	re, _ := regexp.Compile(`Hostname: http-svc.*`)
+	podMap := map[string]bool{}
+
+	for i := 0; i < 100; i++ {
+		_, body, errs := gorequest.New().
+			Get(f.IngressController.HTTPURL).
+			Set("Host", host).
+			End()
+
+		Expect(errs).Should(BeEmpty())
+
+		podName := re.FindString(body)
+		Expect(podName).ShouldNot(Equal(""))
+		podMap[podName] = true
+
+	}
+
+	return podMap
+}
+
+var _ = framework.IngressNginxDescribe("Annotations - UpstreamHashBy", func() {
+	f := framework.NewDefaultFramework("upstream-hash-by")
+
+	BeforeEach(func() {
+		f.NewEchoDeploymentWithReplicas(6)
+	})
+
+	AfterEach(func() {
+	})
+
+	It("should connect to the same pod", func() {
+		annotations := map[string]string{
+			"nginx.ingress.kubernetes.io/upstream-hash-by": "$request_uri",
+		}
+
+		podMap := startIngress(f, &annotations)
+		Expect(len(podMap)).Should(Equal(1))
+
+	})
+
+	It("should connect to the same subset of pods", func() {
+		annotations := map[string]string{
+			"nginx.ingress.kubernetes.io/upstream-hash-by":             "$request_uri",
+			"nginx.ingress.kubernetes.io/upstream-hash-by-subset":      "true",
+			"nginx.ingress.kubernetes.io/upstream-hash-by-subset-size": "3",
+		}
+
+		podMap := startIngress(f, &annotations)
+		Expect(len(podMap)).Should(Equal(3))
+
+	})
+})