文章楔子
在使用Nginx作为前端页面的反向代理时，有时我们需要在服务端为用户的本次访问保存一些临时状态，这种临时状态通常被称为会话。当访问压力增大时，常用的办法是开启多个服务端实例，然后使用Nginx一类的反向代理服务器进行负载均衡。然而对于依赖会话与用户进行交互的页面来说，由于负载均衡可能会将同一用户的两次访问分发到不同的服务端上，这样会话就无法正常运作了。而解决这个问题有最常用的两种方法，一种是在应用层面上作修改，以支持会话共享。另一种方式则是使用会话粘粘：在客户端第一次发起请求时，反向代理为客户端分配一个服务端，并且将该服务端的地址以SetCookie的形式发送给客户端，这样客户端下一次访问该反向代理时，便会带着这个cookie，里面包含了上一次反向代理分配给该客户端的服务端信息。在Nginx中，这种机制是通过一个名为Sticky的插件实现的。而Traefik6.0则集成了与Nginx的Sticky相同功能，并且可以在Kubernetes中方便的开启和配置该特性。
安装Traefik 6.0
首先需要在Kubernetes集群中安装Traefik，如果你已经安装过Traefik请直接跳至第三章
执行下面的yaml文件以安装traefik 6.0和对应的service对象
kind: ClusterRole apiVersion: rbac.authorization.k8s.io/v1beta1 metadata: name: traefik-ingress-controller rules: - apiGroups: - "" resources: - services - endpoints - secrets verbs: - get - list - watch - apiGroups: - extensions resources: - ingresses verbs: - get - list - watch --- kind: ClusterRoleBinding apiVersion: rbac.authorization.k8s.io/v1beta1 metadata: name: traefik-ingress-controller roleRef: apiGroup: rbac.authorization.k8s.io kind: ClusterRole name: traefik-ingress-controller subjects: - kind: ServiceAccount name: traefik-ingress-controller namespace: kube-system --- apiVersion: v1 kind: ServiceAccount metadata: name: traefik-ingress-controller namespace: kube-system --- kind: ConfigMap apiVersion: v1 metadata: name: traefik-conf namespace: kube-system data: traefik.toml: | defaultEntryPoints = ["http"] [entryPoints] [entryPoints.http] address = ":80" --- kind: DaemonSet apiVersion: extensions/v1beta1 metadata: name: traefik-ingress-controller namespace: kube-system labels: k8s-app: traefik-ingress-lb spec: template: metadata: labels: k8s-app: traefik-ingress-lb name: traefik-ingress-lb spec: serviceAccountName: traefik-ingress-controller terminationGracePeriodSeconds: 60 hostNetwork: true - name: config configMap: name: traefik-conf containers: - image: k8s.gcr.io/traefik:1.6 name: traefik-ingress-lb ports: - name: http containerPort: 80 hostPort: 80 - name: admin containerPort: 8080 securityContext: privileged: true args: - --configfile=/config/traefik.toml - -d - --web - --kubernetes volumeMounts: - mountPath: "/config" name: "config" --- kind: Service apiVersion: v1 metadata: name: traefik-ingress-service spec: selector: k8s-app: traefik-ingress-lb ports: - protocol: TCP port: 80 name: web - protocol: TCP port: 8080 name: admin - protocol: TCP port: 443 name: https type: NodePort apiVersion: v1 kind: Service metadata: name: traefik-web-ui namespace: kube-system spec: selector: k8s-app: traefik-ingress-lb ports: - port: 80 targetPort: 8080 --- apiVersion: extensions/v1beta1 kind: Ingress metadata: name: traefik-web-ui namespace: kube-system annotations: kubernetes.io/ingress.class: traefik spec: rules: - host: kuber.ingress.io http: paths: - backend: serviceName: traefik-web-ui servicePort: 80 --- apiVersion: extensions/v1beta1 kind: Ingress metadata: name: traefik-web-ui namespace: kube-system annotations: kubernetes.io/ingress.class: traefik spec: rules: - host: traefik.ingress.io http: paths: - backend: serviceName: traefik-web-ui servicePort: 80
随后将一个非master节点的IP和traefik.ingress.io配置到/etc/hosts文件中，如下图
并在浏览器上访问traefik.ingress.io，即可看到Traefik的监控页面
此时traefik安装完毕。
为服务端开启Sticky
正常的traefik通过下面的配置为指定的后端开启sticky
[backends] [backends.backend1] # Enable sticky session [backends.backend1.loadbalancer.stickiness] # Customize the cookie name # # Optional # Default: a sha1 (6 chars) # # cookieName = "my_cookie"
但此处由于我们将Traefik作为ingress controller安装在kubernetes中，因此Traefik的配置文件是托管给K8s来动态更新的，因此不能通过修改配置文件配置sticky
Kubernetes中可以通过为指定的service对象或ingress对象声明annotation来为ingress controller做额外的详细配置。例如，如果要开启sticky，只需要在想要开启sticky的服务端对应的service上添加以下的annotation即可。
metadata: annotations: traefik.ingress.kubernetes.io/affinity: "true"
还有更多配置可以参考Traefik文档
举例
apiVersion: v1 kind: Service metadata: name: gls namespace: {{ .Release.Namespace }} labels: name: gls annotations: traefik.ingress.kubernetes.io/affinity: "true" traefik.ingress.kubernetes.io/session-cookie-name: "gls-test" traefik.ingress.kubernetes.io/load-balancer-method: drr spec: selector: name: gls ports: - port: 80 targetPort: 8080 --- apiVersion: extensions/v1beta1 kind: Ingress metadata: name: gls namespace: {{ .Release.Namespace }} spec: rules: - host: {{ .Release.Namespace }}.{{ .Values.runtime.network.domainName }} http: paths: - backend: serviceName: gls servicePort: 80 path: /gls
至此Sticky特性开启成功。
本文转自kubernetes中文社区-Kubernetes中使用Traefik的sticky特性
