Kubernetes 服務入口管理與 Nginx Ingress Controller

Kubernetes 具有強大的副本，動態擴容等特性，每一次 Pod 的變化 IP 地址都會發生變化，所以 Kubernetes 引進了 Service 的概念。Kubernetes 中使用 Service 對象抽象出來的機制來管理同一組標簽的 Pod ，而不需要關心 Pod 發生了什么變化並為其分配了一個虛擬的 IP，當外界需要訪問 Pod 里的容器提供的功能時，不直接使用 Pod 的 IP 地址和端口，而是訪問 Service 的這個虛擬 IP 和端口，由 Service 把請求轉發給它背后的 Pod。

Service 暴露服務類型

通常情況下，我們會定義一個 Service 來管理一組 Pod 暴露相關的服務，如果要對外暴露服務的話，只需要定義相應的端口即可（NodePort模式），但如果定義了很多 Service 對象並暴露服務的話就需要配置很多端口，后續維護起來就會變的很復雜，所以 Kubernetes 中還使用了 Ingress 的機制，比如使用 Nginx 綁定一個固定端口 80，后續的請求通過轉發到 Service 即可。這樣如果每次新增服務的話，還需要修改 Nginx 的配置,為了解決這個問題 Kubernetes 中還使用了 Ingress Controller 組件。簡單理解就是原先需要修改 Nginx 配置，然后配置不同的轉發規則到 Service 這個過程抽象出來變成一個 Ingress 對象，后續 Nginx 的變更再通過 Ingress Controoler 與 Kubernetes API 交互，動態的去感知集群中 Ingress 規則變化，再寫到 Nginx Pod 里。

kind: Service
apiVersion: v1
metadata:
  name: test-service
spec:
  selector:
    app: test—-app
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080

由於 Service 中的服務僅可以在容器內部中通訊，如果需要外部能訪問到，還需要暴露 Service , 如下 ：

    internet
        |
  ------------
  [ Services ]

kubernetes 中定義了如下的一些服務類型：

Proxy

使用 Kubernetes 代理來訪問服務，一般內網查看 dashboard，調試遠程查看時可能會用到。

{
  "kind": "Service",
  "apiVersion": "v1",
  "metadata": {
    "name": "kubernetes",
    "namespace": "default",
    "selfLink": "/api/v1/namespaces/default/services/kubernetes",
    "uid": "f594405b-dc19-11e8-90ea-0050569f4a19",
    "resourceVersion": "6",
    "creationTimestamp": "2018-10-30T08:01:08Z",
    "labels": {
      "component": "apiserver",
      "provider": "kubernetes"
    }
  },
  "spec": {
    "ports": [
      {
        "name": "https",
        "protocol": "TCP",
        "port": 443,
        "targetPort": 6443
      }
    ],
    "clusterIP": "10.96.0.1",
    "type": "ClusterIP",
    "sessionAffinity": "None"
  },
  "status": {
    "loadBalancer": {}
  }
}

NodePort Service

指定服務類型為 NodePort 是將外部流量直接發送給服務最原始的方式，需要在 Node 服務節點主機上開放特定的端口，通過綁定主機的某個端口,然后進行 Pod 的請求轉發和負載均衡，但這種方式下缺陷是 Service 可能有很多個，如果每個都綁定一個 Node 主機端口的話，主機需要開放外圍一堆的端口進行服務調用，管理混亂，並且只能使用 30000-32767 之間的端口，適用與臨時暴露某一個服務的端口演示的場景。

{
  "kind": "Service",
  "apiVersion": "v1",
  "metadata": {
    "name": "kubernetes-dashboard",
    "namespace": "kube-system",
    "selfLink": "/api/v1/namespaces/kube-system/services/kubernetes-dashboard",
    "uid": "edd78318-dc1a-11e8-90ea-0050569f4a19",
    "resourceVersion": "1076",
    "creationTimestamp": "2018-10-30T08:08:05Z",
    "labels": {
      "k8s-app": "kubernetes-dashboard"
    }
  },
  "spec": {
    "ports": [
      {
        "protocol": "TCP",
        "port": 443,
        "targetPort": 8443,
        "nodePort": 32151
      }
    ],
    "selector": {
      "k8s-app": "kubernetes-dashboard"
    },
    "clusterIP": "10.103.60.159",
    "type": "NodePort",
    "sessionAffinity": "None",
    "externalTrafficPolicy": "Cluster"
  },
  "status": {
    "loadBalancer": {}
  }
}

LoadBlancer Service

一般配合公用雲使用，指定的端口上的所有流量都將轉發到該服務，使用 LoadBlancer Service 暴露服務時實際上是向雲平台申請創建一個負載均衡器來向外暴露服務，可能需要支付額外的費用。

Nginx Ingress Controller

Nginx Ingress Controller 是由 Nginx 與 Ingress Controller 兩部分組成。

Ingress

與上述的幾種類型不同，Ingress 實際上不是一種服務。它是位於多前面服務的不同，可以轉發不同的域名請求到集群中不同的服務上，簡單的理解，Ingress 就是從 Kubernetes 集群外訪問集群的入口，將用戶的URL請求轉發到不同的 Service 上。Ingress 相當於 Nginx、Apache 等負載均衡方向代理服務器，其中還包括規則定義，即 URL 的路由信息，路由信息得的刷新由 Ingress controller 來提供。

Ingress controller

Ingress Controller 通過不斷地跟 kubernetes API 打交道，實時的感知后端 service、pod 等變化，比如新增和減少 pod，service 增加與減少等；當得到這些變化信息后，Ingress Controller 再結合下文的 Ingress 生成配置，然后更新反向代理負載均衡器，並刷新其配置，達到服務發現的作用。對於 Ingress controller 來說，創建一個 Ingress 相當於在 nginx.conf 中添加一個 server 入口，並 nginx -s reload 重新生效。。

比如想要通過負載均衡器實現不同子域名到不同服務的訪問：

foo.bar.com --|                 |-> foo.bar.com s1:80
              | 178.91.123.132  |
bar.foo.com --|                 |-> bar.foo.com s2:80

定義 Ingress

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: test
spec:
  rules:
  - host: foo.bar.com
    http:
      paths:
      - backend:
          serviceName: s1
          servicePort: 80
  - host: bar.foo.com
    http:
      paths:
      - backend:
          serviceName: s2
          servicePort: 80

Ingress本身並不會自動創建負載均衡器，需要運行一個 Ingress controller 來根據 Ingress 的定義來管理負載均衡器。為了 Ingress 正常工作，集群中必須運行 Ingress controller ,支持 Ingress 的類型的 kube-controller 有如下幾種：

Kubernetes currently supports and maintains GCE and nginx controllers.

F5 Networks provides support and maintenance for the F5 BIG-IP Controller for Kubernetes.

Kong offers community or commercial support and maintenance for the Kong Ingress Controller for Kubernetes

Traefik is a fully featured ingress controller (Let’s Encrypt, secrets, http2, websocket…), and it also comes with commercial support by Containous

NGINX, Inc. offers support and maintenance for the NGINX Ingress Controller for Kubernetes

HAProxy based ingress controller jcmoraisjr/haproxy-ingress which is mentioned on this blog post HAProxy Ingress Controller for Kubernetes

Istio based ingress controller Control Ingress Traffic

如下是第三方 Nginx 支持的模式 NGINX Ingress Controller for Kubernetes ，非官方（雖然官方也依賴開源版本的 Nginx）。

關於 nginxinc/kubernetes-ingress 與 kubernetes/ingress-nginx 兩者的差異: https://github.com/nginxinc/kubernetes-ingress/blob/master/docs/nginx-ingress-controllers.md ，如果不是使用的不是 NGINX Plus 商業版本，還是官方的支持要豐富一些，另外基於軟件的 Traefik，HAProxy，Kong 也是不錯的選擇，不差錢的也可以考慮商業性質的硬件負載設備如 F5 等。個人比較看好 kubernetes/ingress-nginx 與 Traefik 。這里選擇使用官方的 kubernetes/ingress-nginx 作為 ingress controller ，后續再嘗試其他第三方的組件。

安裝 nginx-ingress-controller (host network 模式根據 Node 數量設置副本數，取決於部署的方式 Deployment or DaemonSet)

$ kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/master/deploy/mandatory.yaml
$ kubectl -n ingress-nginx get pod -o wide
NAME                                        READY   STATUS    RESTARTS   AGE   IP          NODE                NOMINATED NODE
nginx-ingress-controller-5bdbdc5657-bcn2f   1/1     Running   0          74m   10.38.0.1   kubernetes-node-2   <none>
nginx-ingress-controller-5bdbdc5657-mmtph   1/1     Running   0          79m   10.40.0.1   kubernetes-node-1   <none>
$ kubectl get pods --all-namespaces -l app.kubernetes.io/name=ingress-nginx --watch
NAMESPACE       NAME                                        READY   STATUS    RESTARTS   AGE
ingress-nginx   nginx-ingress-controller-6457d975c8-6twqf   1/1     Running   0          78m
ingress-nginx   nginx-ingress-controller-5bdbdc5657-mmtph   1/1     Running   0          83m

$ kubectl describe pod nginx-ingress-controller-6457d975c8-6twqf -n ingress-nginx
Name:               nginx-ingress-controller-6457d975c8-6twqf
Namespace:          ingress-nginx
Priority:           0
PriorityClassName:  <none>
Node:               kubernetes-node-2/172.23.216.50
Start Time:         Wed, 31 Oct 2018 20:04:44 +0800
Labels:             app.kubernetes.io/name=ingress-nginx
                    app.kubernetes.io/part-of=ingress-nginx
                    pod-template-hash=6457d975c8
Annotations:        prometheus.io/port: 10254
                    prometheus.io/scrape: true
Status:             Running
IP:                 172.23.216.50
Controlled By:      ReplicaSet/nginx-ingress-controller-6457d975c8
Containers:
  nginx-ingress-controller:
    Container ID:  docker://f4d5b69cf579752799d6d7e92c547ed9a5a0ba9154b3683c4956079ea9e77304
    Image:         quay.io/kubernetes-ingress-controller/nginx-ingress-controller:0.20.0
    Image ID:      docker-pullable://quay.io/kubernetes-ingress-controller/nginx-ingress-controller@sha256:f6180c5397d2361c317aff1314dc192ab0f9f515346a5319422cdc264f05d2d9
    Ports:         80/TCP, 443/TCP
    Host Ports:    80/TCP, 443/TCP
    Args:
      /nginx-ingress-controller
      --configmap=$(POD_NAMESPACE)/nginx-configuration
      --publish-service=$(POD_NAMESPACE)/ingress-nginx
      --annotations-prefix=nginx.ingress.kubernetes.io
    State:          Running
      Started:      Wed, 31 Oct 2018 20:04:45 +0800
    Ready:          True
    Restart Count:  0
    Liveness:       http-get http://:10254/healthz delay=10s timeout=1s period=10s #success=1 #failure=3
    Readiness:      http-get http://:10254/healthz delay=0s timeout=1s period=10s #success=1 #failure=3
    Environment:
      POD_NAME:       nginx-ingress-controller-6457d975c8-6twqf (v1:metadata.name)
      POD_NAMESPACE:  ingress-nginx (v1:metadata.namespace)
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from nginx-ingress-serviceaccount-token-rhpsb (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             True 
  ContainersReady   True 
  PodScheduled      True 
Volumes:
  nginx-ingress-serviceaccount-token-rhpsb:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  nginx-ingress-serviceaccount-token-rhpsb
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type     Reason            Age                From                        Message
  ----     ------            ----               ----                        -------
  Warning  FailedScheduling  49m (x3 over 49m)  default-scheduler           0/3 nodes are available: 1 node(s) had taints that the pod didn't tolerate, 2 node(s) didn't have free ports for the requested pod ports.
  Normal   Scheduled         49m                default-scheduler           Successfully assigned ingress-nginx/nginx-ingress-controller-6457d975c8-6twqf to kubernetes-node-2
  Normal   Pulled            48m                kubelet, kubernetes-node-2  Container image "quay.io/kubernetes-ingress-controller/nginx-ingress-controller:0.20.0" already present on machine
  Normal   Created           48m                kubelet, kubernetes-node-2  Created container
  Normal   Started           48m                kubelet, kubernetes-node-2  Started container

查看安裝的版本

POD_NAMESPACE=ingress-nginx
POD_NAME=$(kubectl get pods -n $POD_NAMESPACE -l app.kubernetes.io/name=ingress-nginx -o jsonpath='{.items[0].metadata.name}')
kubectl exec -it $POD_NAME -n $POD_NAMESPACE -- /nginx-ingress-controller --version

-------------------------------------------------------------------------------
NGINX Ingress controller
  Release:    0.20.0
  Build:      git-e8d8103
  Repository: https://github.com/kubernetes/ingress-nginx.git
-------------------------------------------------------------------------------

根據不同的網絡環境與場景，需要選擇不同的策略，具體可以參考官方的文檔，如下列舉常用的幾種：

Cloud environments 模式

如果是使用公有雲，可以使用公有雲的負載到 Node 節點即可，需要支付額外費用。

NodePort Service 模式（臨時測試,一般不建議使用）

apiVersion: v1
kind: Service
metadata:
  name: ingress-nginx
  namespace: ingress-nginx
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx
spec:
  type: NodePort
  ports:
    - name: http
      port: 80
      targetPort: 80

# nodePort: 30000
      protocol: TCP
    - name: https
      port: 443
      targetPort: 443
      protocol: TCP
  selector:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx

---

執行

$ kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/master/deploy/provider/baremetal/service-nodeport.yaml
$ kubectl -n ingress-nginx get svc
NAME            TYPE       CLUSTER-IP    EXTERNAL-IP   PORT(S)                      AGE
ingress-nginx   NodePort   10.98.42.64   <none>        80:31460/TCP,443:31200/TCP   6m50s

host network 模式

修改 hostNetwork: true

vi nginx-ingress-controller.yaml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx-ingress-controller
  namespace: ingress-nginx
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx
spec:
  replicas: 2
  selector:
    matchLabels:
      app.kubernetes.io/name: ingress-nginx
      app.kubernetes.io/part-of: ingress-nginx
  template:
    metadata:
      labels:
        app.kubernetes.io/name: ingress-nginx
        app.kubernetes.io/part-of: ingress-nginx
      annotations:
        prometheus.io/port: "10254"
        prometheus.io/scrape: "true"
    spec:
      hostNetwork: true
      serviceAccountName: nginx-ingress-serviceaccount
      containers:
        - name: nginx-ingress-controller
          image: quay.io/kubernetes-ingress-controller/nginx-ingress-controller:0.20.0
          args:
            - /nginx-ingress-controller
            - --configmap=$(POD_NAMESPACE)/nginx-configuration
            - --publish-service=$(POD_NAMESPACE)/ingress-nginx
            - --annotations-prefix=nginx.ingress.kubernetes.io
          securityContext:
            capabilities:
              drop:
                - ALL
              add:
                - NET_BIND_SERVICE
            # www-data -> 33
            runAsUser: 33
          env:
            - name: POD_NAME
              valueFrom:
                fieldRef:
                  fieldPath: metadata.name
            - name: POD_NAMESPACE
              valueFrom:
                fieldRef:
                  fieldPath: metadata.namespace
          ports:
            - name: http
              containerPort: 80
            - name: https
              containerPort: 443
          livenessProbe:
            failureThreshold: 3
            httpGet:
              path: /healthz
              port: 10254
              scheme: HTTP
            initialDelaySeconds: 10
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 1
          readinessProbe:
            failureThreshold: 3
            httpGet:
              path: /healthz
              port: 10254
              scheme: HTTP
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 1

---

$ kubectl apply -f nginx-ingress-controller.yaml

查看 ingress-nginx

$ kubectl -n ingress-nginx get pod -o wide
NAME                                        READY   STATUS    RESTARTS   AGE    IP              NODE                NOMINATED NODE
nginx-ingress-controller-6457d975c8-6twqf   1/1     Running   0          3m7s   172.23.216.50   kubernetes-node-2   <none>
nginx-ingress-controller-6457d975c8-smjsv   1/1     Running   0          3m7s   172.23.216.49   kubernetes-node-1   <none>

測試訪問

$ curl -D- 172.23.216.50
HTTP/1.1 404 Not Found
Server: nginx/1.15.5
Date: Wed, 31 Oct 2018 12:08:40 GMT
Content-Type: text/html
Content-Length: 153
Connection: keep-alive

<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.15.5</center>
</body>
</html>

創建 kubernetes-dashboard-ingress（默認 https ，annotations 頭必須設置 ）

vi kubernetes-dashboard-ingress.yaml

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: kubernetes-dashboard-ingress
  namespace: kube-system
  annotations:
    nginx.ingress.kubernetes.io/ssl-redirect: "true"
    nginx.ingress.kubernetes.io/rewrite-target: /
    nginx.ingress.kubernetes.io/secure-backends: "true"

spec:
#  tls:
#   - secretName: k8s-dashboard-secret
  rules:
   - http:
      paths:
      - path: /
        backend:
          serviceName: kubernetes-dashboard
          servicePort: 443
      - path: /test
        backend:
          serviceName: test-nginx
          servicePort: 80

執行
  
  
  
          
 
           
$ kubectl apply -f kubernetes-dashboard-ingress.yaml
$ kubectl get ingress -o wide --all-namespaces      
NAMESPACE     NAME                           HOSTS   ADDRESS   PORTS   AGE
kube-system   kubernetes-dashboard-ingress   *                 80      3h53m
 
          

最后訪問：https://172.23.216.49/ 或 https://172.23.216.50/

備注：其他功能參考官方文檔：

• Ingress Path Matching
• baremetal
• monitoring

其他命令
  
  
  
          
 
           
#刪除 Ingress Controller 命名空間
$ kubectl delete namespace nginx-ingress
#安裝網絡組件
$ yum install net-tools
#查看開放的端口
$ netstat -ntlp
 
          

REFER:
https://kubernetes.io/docs/concepts/services-networking/ingress/
https://medium.com/google-cloud/kubernetes-nodeport-vs-loadbalancer-vs-ingress-when-should-i-use-what-922f010849e0
https://www.nginx.com/products/nginx/kubernetes-ingress-controller
https://github.com/kubernetes/ingress-nginx
https://github.com/containous/traefik
https://github.com/nginxinc/kubernetes-ingress/
https://my.oschina.net/u/2306127/blog/1930169