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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