Keepalived-VIP

Kubernetes 使用 keepalived 来产生虚拟 IP address
我们将探讨如何利用 IPVS - The Linux Virtual Server Project" 来 kubernetes 配置 VIP
前言
kubernetes v1.6 版提供了三种方式去暴露 Service：
1.
L4 的 LoadBalacncer : 只能在 cloud providers 上被使用 像是 GCE 或 AWS
2.
NodePort : NodePort 允许在每个节点上开启一个 port 口, 借由这个 port 口会再将请求导向到随机的 pod 上
3.
L7 Ingress :Ingress 为一个 LoadBalancer(例: nginx, HAProxy, traefik, vulcand) 会将 HTTP/HTTPS 的各个请求导向到相对应的 service endpoint
有了这些方式, 为何我们还需要 keepalived ?
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                                                  ___________________
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                                                 |                   |
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                                           |-----| Host IP: 10.4.0.3 |
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                                           |     |___________________|
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                                           |
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                                           |      ___________________
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                                           |     |                   |
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Public ----(example.com = 10.4.0.3/4/5)----|-----| Host IP: 10.4.0.4 |
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                                           |     |___________________|
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                                           |
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                                           |      ___________________
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                                           |     |                   |
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                                           |-----| Host IP: 10.4.0.5 |
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                                                 |___________________|
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我们假设 Ingress 运行在 3 个 kubernetes 节点上, 并对外暴露 10.4.0.x 的 IP 去做 loadbalance
DNS Round Robin (RR) 将对应到 example.com 的请求轮循给这 3 个节点, 如果 10.4.0.3 掛了, 仍有三分之一的流量会导向 10.4.0.3, 这样就会有一段 downtime, 直到 DNS 发现 10.4.0.3 掛了并修正导向
严格来说, 这并没有真正的做到 High Availability (HA)
这边 IPVS 可以帮助我们解决这件事, 这个想法是虚拟 IP(VIP) 对应到每个 service 上, 并将 VIP 暴露到 kubernetes 群集之外
与 service-loadbalancer 或 ingress-nginx 的区别
我们看到以下的图
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                                               ___________________
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                                              |                   |
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                                              | VIP: 10.4.0.50    |
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                                        |-----| Host IP: 10.4.0.3 |
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                                        |     | Role: Master      |
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                                        |     |___________________|
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                                        |
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                                        |      ___________________
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                                        |     |                   |
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                                        |     | VIP: Unassigned   |
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Public ----(example.com = 10.4.0.50)----|-----| Host IP: 10.4.0.4 |
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                                        |     | Role: Slave       |
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                                        |     |___________________|
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                                        |
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                                        |      ___________________
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                                        |     |                   |
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                                        |     | VIP: Unassigned   |
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                                        |-----| Host IP: 10.4.0.5 |
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                                              | Role: Slave       |
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                                              |___________________|
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我们可以看到只有一个 node 被选为 Master(透过 VRRP 选择的), 而我们的 VIP 是 10.4.0.50, 如果 10.4.0.3 掛掉了, 那会从剩余的节点中选一个成为 Master 并接手 VIP, 这样我们就可以确保落实真正的 HA
环境需求
只需要确认要运行 keepalived-vip 的 kubernetes 群集 DaemonSets 功能是正常的就行了
RBAC
由于 kubernetes 在 1.6 后引进了 RBAC 的概念, 所以我们要先去设定 rule, 至於有关 RBAC 的详情请至 说明。
vip-rbac.yaml
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apiVersion: rbac.authorization.k8s.io/v1beta1
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kind: ClusterRole
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metadata:
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  name: kube-keepalived-vip
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rules:
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- apiGroups: [""]
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  resources:
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  - pods
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  - nodes
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  - endpoints
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  - services
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  - configmaps
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  verbs: ["get", "list", "watch"]
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---
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apiVersion: v1
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kind: ServiceAccount
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metadata:
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  name: kube-keepalived-vip
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  namespace: default
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---
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apiVersion: rbac.authorization.k8s.io/v1beta1
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kind: ClusterRoleBinding
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metadata:
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  name: kube-keepalived-vip
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roleRef:
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  apiGroup: rbac.authorization.k8s.io
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  kind: ClusterRole
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  name: kube-keepalived-vip
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subjects:
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- kind: ServiceAccount
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  name: kube-keepalived-vip
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  namespace: default
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clusterrolebinding.yaml
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apiVersion: rbac.authorization.k8s.io/v1alpha1
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kind: ClusterRoleBinding
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metadata:
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  name: kube-keepalived-vip
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roleRef:
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  apiGroup: rbac.authorization.k8s.io
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  kind: ClusterRole
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  name: kube-keepalived-vip
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subjects:
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  - kind: ServiceAccount
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    name: kube-keepalived-vip
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    namespace: default
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$ kubectl create -f vip-rbac.yaml
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$ kubectl create -f clusterrolebinding.yaml
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示例
先建立一个简单的 service
nginx-deployment.yaml
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apiVersion: apps/v1beta1
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kind: Deployment
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metadata:
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  name: nginx-deployment
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spec:
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  replicas: 3
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  template:
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    metadata:
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      labels:
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        app: nginx
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    spec:
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      containers:
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      - name: nginx
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        image: nginx:1.7.9
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        ports:
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        - containerPort: 80
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---
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apiVersion: v1
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kind: Service
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metadata:
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  name: nginx
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  labels:
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    app: nginx
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spec:
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  type: NodePort
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  ports:
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  - port: 80
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    nodePort: 30302
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    targetPort: 80
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    protocol: TCP
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    name: http
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  selector:
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    app: nginx
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主要功能就是 pod 去监听听 80 port, 再开启 service NodePort 监听 30320
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$ kubecrl create -f nginx-deployment.yaml
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接下来我们要做的是 config map
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$ echo "apiVersion: v1
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kind: ConfigMap
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metadata:
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  name: vip-configmap
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data:
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  10.87.2.50: default/nginx" | kubectl create -f -
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注意, 这边的 10.87.2.50 必须换成你自己同网段下无使用的 IP e.g. 10.87.2.X 后面 nginx 为 service 的 name, 这边可以自行更换
接着确认一下
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$kubectl get configmap
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NAME            DATA      AGE
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vip-configmap   1         23h
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再来就是设置 keepalived-vip
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apiVersion: extensions/v1beta1
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kind: DaemonSet
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metadata:
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  name: kube-keepalived-vip
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spec:
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  template:
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    metadata:
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      labels:
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        name: kube-keepalived-vip
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    spec:
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      hostNetwork: true
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      containers:
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        - image: gcr.io/google_containers/kube-keepalived-vip:0.9
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          name: kube-keepalived-vip
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          imagePullPolicy: Always
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          securityContext:
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            privileged: true
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          volumeMounts:
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            - mountPath: /lib/modules
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              name: modules
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              readOnly: true
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            - mountPath: /dev
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              name: dev
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          # use downward API
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          env:
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            - name: POD_NAME
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              valueFrom:
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                fieldRef:
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                  fieldPath: metadata.name
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            - name: POD_NAMESPACE
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              valueFrom:
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                fieldRef:
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                  fieldPath: metadata.namespace
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          # to use unicast
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          args:
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          - --services-configmap=default/vip-configmap
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          # unicast uses the ip of the nodes instead of multicast
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          # this is useful if running in cloud providers (like AWS)
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          #- --use-unicast=true
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      volumes:
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        - name: modules
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          hostPath:
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            path: /lib/modules
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        - name: dev
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          hostPath:
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            path: /dev
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建立 daemonset
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$ kubectl get daemonset kube-keepalived-vip
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NAME                  DESIRED   CURRENT   READY     UP-TO-DATE   AVAILABLE   NODE-SELECTOR   AGE
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kube-keepalived-vip   5         5         5         5            5
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检查一下配置状态
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kubectl get pod -o wide |grep keepalive
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kube-keepalived-vip-c4sxw         1/1       Running            0          23h       10.87.2.6    10.87.2.6
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kube-keepalived-vip-c9p7n         1/1       Running            0          23h       10.87.2.8    10.87.2.8
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kube-keepalived-vip-psdp9         1/1       Running            0          23h       10.87.2.10   10.87.2.10
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kube-keepalived-vip-xfmxg         1/1       Running            0          23h       10.87.2.12   10.87.2.12
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kube-keepalived-vip-zjts7         1/1       Running            3          23h       10.87.2.4    10.87.2.4
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可以随机挑一个 pod, 去看里面的配置
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 $ kubectl exec kube-keepalived-vip-c4sxw cat /etc/keepalived/keepalived.conf
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​
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​
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global_defs {
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  vrrp_version 3
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  vrrp_iptables KUBE-KEEPALIVED-VIP
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}
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​
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vrrp_instance vips {
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  state BACKUP
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  interface eno1
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  virtual_router_id 50
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  priority 103
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  nopreempt
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  advert_int 1
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​
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  track_interface {
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    eno1
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  }
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​
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​
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​
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  virtual_ipaddress {
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    10.87.2.50
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  }
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}
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​
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​
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# Service: default/nginx
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virtual_server 10.87.2.50 80 { // 此为 service 开的口
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  delay_loop 5
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  lvs_sched wlc
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  lvs_method NAT
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  persistence_timeout 1800
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  protocol TCP
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​
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​
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  real_server 10.2.49.30 8080 { // 这里说明 pod 的真实状况
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    weight 1
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    TCP_CHECK {
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      connect_port 80
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      connect_timeout 3
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    }
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  }
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​
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}
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最后我们去测试这功能
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$ curl  10.87.2.50
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<!DOCTYPE html>
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<html>
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<head>
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<title>Welcome to nginx!</title>
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<style>
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    body {
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        width: 35em;
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        margin: 0 auto;
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        font-family: Tahoma, Verdana, Arial, sans-serif;
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    }
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</style>
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</head>
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<body>
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<h1>Welcome to nginx!</h1>
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<p>If you see this page, the nginx web server is successfully installed and
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working. Further configuration is required.</p>
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​
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<p>For online documentation and support please refer to
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<a href="http://nginx.org/">nginx.org</a>.<br/>
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Commercial support is available at
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<a href="http://nginx.com/">nginx.com</a>.</p>
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​
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<p><em>Thank you for using nginx.</em></p>
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</body>
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</html>
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10.87.2.50:80(我们假设的 VIP, 实际上其实没有 node 是用这 IP) 即可帮我们导向这个 service
以上的程式代码都在 github 上可以找到。
参考文档
​kweisamx/kubernetes-keepalived-vip​
​kubernetes/keepalived-vip​

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前言

与 service-loadbalancer 或 ingress-nginx 的区别