Ingress是什么？

在 Kubernetes 集群中，Ingress是授权入站连接到达集群服务的规则集合，提供七层负载均衡能力。可以给 Ingress 配置提供外部可访问的 URL、负载均衡、SSL、基于名称的虚拟主机等。简单来说Ingress说一些规则集合，这些规则可以实现url到Kubernetes中的service这一层的路由功能。既然Ingress只是规则，那么这些规则的具体实现是怎么样的呢？是有Ingress-Controller来实现的，目前比较常见使用较多的是Nginx-Ingress-Controller。

可以这样理解一下，nginx-ingress-controller是一个nginx应用，它能干什么呢？它能代理后端的service，它能根据Ingress的配置，将对应的配置翻译成nginx应用的配置，来实现七层路由的功能。既然nginx-ingress-controller是作为一个类似网关的这么一个应用，那么我的nginx-ingress-controller这个应用本身就是需要在集群外能够访问到的，那么我是需要对外暴露nginx-ingress-controller这个应用的，在k8s中是通过创建一个LoadBalancer的Service：nginx-ingress-lb来暴露nginx-ingress-controller这个应用的。对应的，我们也就知道了nginx-ingress-controller这个应用从外部访问是通过nginx-ingress-lb这个service关联的SLB（负载均衡产品）来进行的。至于对应的slb的相关配置策略可以参考一下之前的文章，关于服务实现的内容。

简单的请求链路如下：

客户端 --> slb --> nginx-ingress-lb service --> nginx-ingress-controller pod --> app service --> app pod

我们使用Ingress来暴露服务，那么需要创建对应的资源，要想功能正常，nginx-ingress-controller的pod需要正常运行，nginx-ingress-lb service和slb监听配置正常才行，Ingress要关联的后端应用服务也是需要配置正确，包括应用pod运行正常，应用的service配置正确。

然后我们需要创建对应的Ingress来实现我们的需求。我们先创建一个简单的Ingress来大体看下具体的功能是什么样子的。我们这条Ingress的目的要实现：请求域名：ingress.test.com，实际请求会到后端的tomcat应用中。

相关配置：

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  labels:
    app: tomcat
  name: tomcat
  namespace: default
spec:
  progressDeadlineSeconds: 600
  replicas: 1
  revisionHistoryLimit: 10
  selector:
    matchLabels:
      app: tomcat
  strategy:
    rollingUpdate:
      maxSurge: 25%
      maxUnavailable: 25%
    type: RollingUpdate
  template:
    metadata:
      labels:
        app: tomcat
    spec:
      containers:
        - image: 'tomcat:latest'
          imagePullPolicy: Always
          name: tomcat
          resources:
            requests:
              cpu: 100m
              memory: 200Mi
          terminationMessagePath: /dev/termination-log
          terminationMessagePolicy: File
      dnsPolicy: ClusterFirst
      restartPolicy: Always
      schedulerName: default-scheduler
      securityContext: {}
      terminationGracePeriodSeconds: 30
---
apiVersion: v1
kind: Service
metadata:
  name: tomcat-svc
  namespace: default
spec:
  clusterIP: 172.21.6.143
  ports:
    - port: 8080
      protocol: TCP
      targetPort: 8080 #service常见配置错误的地方，targetPort必须是pod暴露的端口，不能是其他的
  selector:
    app: tomcat
  sessionAffinity: None
  type: ClusterIP
---
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: tomcat
  namespace: default
spec:
  rules:
    - host: ingress.test.com
      http:
        paths:
          - backend:
              serviceName: tomcat-svc
              servicePort: 8080
            path: /

在Ingress创建成功后会自动生成一个端点IP，我们应该将域名：ingress.test.com做A记录解析到这个端点IP。这样我们访问域名：ingress.test.com，实际请求会请求到我们的tomcat应用。

测试结果：

#curl http://端点IP -H "host:ingress.test.com" -I
HTTP/1.1 200 
Date: Thu, 26 Sep 2019 04:55:39 GMT
Content-Type: text/html;charset=UTF-8
Connection: keep-alive
Vary: Accept-Encoding

nginx-ingress-controller 配置分析

yaml如下：

apiVersion: apps/v1beta2
kind: Deployment
metadata:
  labels:
    app: ingress-nginx
  name: nginx-ingress-controller
  namespace: kube-system
spec:
  progressDeadlineSeconds: 600
  replicas: 2
  revisionHistoryLimit: 10
  selector:
    matchLabels:
      app: ingress-nginx
  strategy:
    rollingUpdate:
      maxSurge: 25%
      maxUnavailable: 25%
    type: RollingUpdate
  template:
    metadata:
      annotations:
        prometheus.io/port: '10254'
        prometheus.io/scrape: 'true'
      labels:
        app: ingress-nginx
    spec:
      affinity:
        podAntiAffinity:
          preferredDuringSchedulingIgnoredDuringExecution:
            - podAffinityTerm:
                labelSelector:
                  matchExpressions:
                    - key: app
                      operator: In
                      values:
                        - ingress-nginx
                topologyKey: kubernetes.io/hostname
              weight: 100
      containers:
        - args:
            - /nginx-ingress-controller
            - '--configmap=$(POD_NAMESPACE)/nginx-configuration'
            - '--tcp-services-configmap=$(POD_NAMESPACE)/tcp-services'
            - '--udp-services-configmap=$(POD_NAMESPACE)/udp-services'
            - '--annotations-prefix=nginx.ingress.kubernetes.io'
            - '--publish-service=$(POD_NAMESPACE)/nginx-ingress-lb'
            - '--v=2'
          env:
            - name: POD_NAME
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: metadata.name
            - name: POD_NAMESPACE
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: metadata.namespace
          image: >-
            registry-vpc.cn-shenzhen.aliyuncs.com/acs/aliyun-ingress-controller:v0.22.0.5-552e0db-aliyun
          imagePullPolicy: IfNotPresent
          livenessProbe:
            failureThreshold: 3
            httpGet:
              path: /healthz
              port: 10254
              scheme: HTTP
            initialDelaySeconds: 10
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 1
          name: nginx-ingress-controller
          ports:
            - containerPort: 80
              name: http
              protocol: TCP
            - containerPort: 443
              name: https
              protocol: TCP
          readinessProbe:
            failureThreshold: 3
            httpGet:
              path: /healthz
              port: 10254
              scheme: HTTP
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 1
          resources: {}
          securityContext:
            capabilities:
              add:
                - NET_BIND_SERVICE
              drop:
                - ALL
            procMount: Default
            runAsUser: 33
          terminationMessagePath: /dev/termination-log
          terminationMessagePolicy: File
          volumeMounts:
            - mountPath: /etc/localtime
              name: localtime
              readOnly: true
      dnsPolicy: ClusterFirst
      initContainers:
        - command:
            - /bin/sh
            - '-c'
            - |
              sysctl -w net.core.somaxconn=65535
              sysctl -w net.ipv4.ip_local_port_range="1024 65535"
              sysctl -w fs.file-max=1048576
              sysctl -w fs.inotify.max_user_instances=16384
              sysctl -w fs.inotify.max_user_watches=524288
              sysctl -w fs.inotify.max_queued_events=16384
          image: 'registry-vpc.cn-shenzhen.aliyuncs.com/acs/busybox:latest'
          imagePullPolicy: Always
          name: init-sysctl
          resources: {}
          securityContext:
            privileged: true
            procMount: Default
          terminationMessagePath: /dev/termination-log
          terminationMessagePolicy: File
      nodeSelector:
        beta.kubernetes.io/os: linux
      restartPolicy: Always
      schedulerName: default-scheduler
      securityContext: {}
      serviceAccount: nginx-ingress-controller
      serviceAccountName: nginx-ingress-controller
      terminationGracePeriodSeconds: 30
      volumes:
        - hostPath:
            path: /etc/localtime
            type: File
          name: localtime
---
apiVersion: v1
kind: Service
metadata:
  labels:
    app: nginx-ingress-lb
  name: nginx-ingress-lb
  namespace: kube-system
spec:
  clusterIP: 172.21.11.181
  externalTrafficPolicy: Local
  healthCheckNodePort: 32435
  ports:
    - name: http
      nodePort: 31184
      port: 80
      protocol: TCP
      targetPort: 80
    - name: https
      nodePort: 31972
      port: 443
      protocol: TCP
      targetPort: 443
  selector:
    app: ingress-nginx
  sessionAffinity: None
  type: LoadBalancer

其中需要特别注意的配置是容器的args配置：

• --configmap=$(POD_NAMESPACE)/nginx-configuration 表明nginx-ingress-controller使用是哪个namespace下configmap来读取nginx-ingress-controller的nginx配置。默认是使用kube-system/nginx-configuration这个configmap。
• --publish-service=$(POD_NAMESPACE)/nginx-ingress-lb 表明选择使用nginx-ingress-controller的Ingress的端点地址是使用的哪一个LoadBalancer的Service的扩展IP。默认是使用kube-system/nginx-ingress-lb这个Service。
• --ingress-class=INGRESS_CLASS 这个配置是对nginx-ingress-controller自身的一个标识，表示我是谁，没有配置就是默认的“nginx”。这个配置有什么用呢？是用来让Ingress选择我要使用的ingress-controller是谁，Ingress通过注解：kubernetes.io/ingress.class: ""决定选择哪一个ingress-controller，如果没有配置那么就是选择--ingress-class=“nginx”这个ingress-controller。

如何在一个阿里云kubernetes集群里面部署多套Nginx Ingress Controller参考文档：

https://yq.aliyun.com/articles/645856

之前我们也说了Ingress是规则，会下发到ingress-controller实现相关功能，那我们就来看下下发到ingress-controller的配置究竟是什么样。我们可以进入到nginx-ingress-controller的pod内来查看一下nginx配置。在pod内的/etc/nginx/nginx.conf里面，除了一些公共的配置外，上面的Ingress生成了如下的nginx.conf配置：

## start server ingress.test.com
    server {
        server_name ingress.test.com ;
        
        listen 80;
        
        set $proxy_upstream_name "-";
        
        location / {
            
            set $namespace      "default";
            set $ingress_name   "tomcat";
            set $service_name   "tomcat-svc";
            set $service_port   "8080";
            set $location_path  "/";
            
            rewrite_by_lua_block {
                balancer.rewrite()
            }
            
            access_by_lua_block {
                balancer.access()
            }
            
            header_filter_by_lua_block {
                
            }
            body_filter_by_lua_block {
                
            }
            
            log_by_lua_block {
                
                balancer.log()
                
                monitor.call()
                
            }
            
            port_in_redirect off;
            
            set $proxy_upstream_name    "default-tomcat-svc-8080";
            set $proxy_host             $proxy_upstream_name;
            
            client_max_body_size                    100m;
            
            proxy_set_header Host                   $best_http_host;
            
            # Pass the extracted client certificate to the backend
            
            # Allow websocket connections
            proxy_set_header                        Upgrade           $http_upgrade;
            
            proxy_set_header                        Connection        $connection_upgrade;
            
            proxy_set_header X-Request-ID           $req_id;
            proxy_set_header X-Real-IP              $the_real_ip;
            
            proxy_set_header X-Forwarded-For        $the_real_ip;
            
            proxy_set_header X-Forwarded-Host       $best_http_host;
            proxy_set_header X-Forwarded-Port       $pass_port;
            proxy_set_header X-Forwarded-Proto      $pass_access_scheme;
            
            proxy_set_header X-Original-URI         $request_uri;
            
            proxy_set_header X-Scheme               $pass_access_scheme;
            
            # Pass the original X-Forwarded-For
            proxy_set_header X-Original-Forwarded-For $http_x_forwarded_for;
            
            # mitigate HTTPoxy Vulnerability
            # https://www.nginx.com/blog/mitigating-the-httpoxy-vulnerability-with-nginx/
            proxy_set_header Proxy                  "";
            
            # Custom headers to proxied server
            
            proxy_connect_timeout                   10s;
            proxy_send_timeout                      60s;
            proxy_read_timeout                      60s;
            
            proxy_buffering                         off;
            proxy_buffer_size                       4k;
            proxy_buffers                           4 4k;
            proxy_request_buffering                 on;
            
            proxy_http_version                      1.1;
            
            proxy_cookie_domain                     off;
            proxy_cookie_path                       off;
            
            # In case of errors try the next upstream server before returning an error
            proxy_next_upstream                     error timeout;
            proxy_next_upstream_tries               3;
            
            proxy_pass http://upstream_balancer;
            
            proxy_redirect                          off;
            
        }
        
    }
    ## end server ingress.test.com

Nginx.conf里面的配置比较多，这里就不在一一详解，后续我们再针对一些常见的功能配置进行说明。

同时最新版本的nginx-ingress-controller已经默认开启了Upstream的动态更新，可以在nginx-ingress-controller的pod内请求：curl http://127.0.0.1:18080/configuration/backends 查看。具体内容如下：

[{"name":"default-tomcat-svc-8080","service":{"metadata":{"creationTimestamp":null},"spec":{"ports":[{"protocol":"TCP","port":8080,"targetPort":8080}],"selector":{"app":"tomcat"},"clusterIP":"172.21.6.143","type":"ClusterIP","sessionAffinity":"None"},"status":{"loadBalancer":{}}},"port":8080,"secureCACert":{"secret":"","caFilename":"","pemSha":""},"sslPassthrough":false,"endpoints":[{"address":"172.20.2.141","port":"8080"}],"sessionAffinityConfig":{"name":"","cookieSessionAffinity":{"name":"","hash":""}},"upstreamHashByConfig":{"upstream-hash-by-subset-size":3},"noServer":false,"trafficShapingPolicy":{"weight":0,"header":"","cookie":""}},{"name":"upstream-default-backend","port":0,"secureCACert":{"secret":"","caFilename":"","pemSha":""},"sslPassthrough":false,"endpoints":[{"address":"127.0.0.1","port":"8181"}],"sessionAffinityConfig":{"name":"","cookieSessionAffinity":{"name":"","hash":""}},"upstreamHashByConfig":{},"noServer":false,"trafficShapingPolicy":{"weight":0,"header":"","cookie":""}}]

我们可以看到这里有ingress关联的service及其endpoint的映射关系，这样可以就可以请求到具体的pod的业务了。

路由配置的动态更新可以参考文档了解一下：https://yq.aliyun.com/articles/692732

在后续的文章我们再详细讲一些常见的使用场景。