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
kubernetes v1.6 版提供了三种方式去暴露 Service：
- L4 的 LoadBalacncer : 只能再 cloud providers 上被使用 像是 GCE 或 AWS
- NodePort : NodePort 允许再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
- 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 ?
___________________
| |
|-----| Host IP: 10.4.0.3 |
| |___________________|
|
| ___________________
| | |
Public ----(example.com = 10.4.0.3/4/5)----|-----| Host IP: 10.4.0.4 |
| |___________________|
|
| ___________________
| | |
|-----| Host IP: 10.4.0.5 |
|___________________|
我们假设 Ingress 运行再 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 nginx 的区别
我们看到以下的图
___________________
| |
| VIP: 10.4.0.50 |
|-----| Host IP: 10.4.0.3 |
| | Role: Master |
| |___________________|
|
| ___________________
| | |
| | VIP: Unassigned |
Public ----(example.com = 10.4.0.50)----|-----| Host IP: 10.4.0.3 |
| | Role: Slave |
| |___________________|
|
| ___________________
| | |
| | VIP: Unassigned |
|-----| Host IP: 10.4.0.3 |
| Role: Slave |
|___________________|
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
只需要确认要运行 keepalived-vip 的 kubernetes 群集 DaemonSets 功能是正常的就行了
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
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRole
metadata:
name: kube-keepalived-vip
rules:
- apiGroups: [""]
resources:
- pods
- nodes
- endpoints
- services
- configmaps
verbs: ["get", "list", "watch"]
---
apiVersion: v1
kind: ServiceAccount
metadata:
name: kube-keepalived-vip
namespace: default
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
name: kube-keepalived-vip
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: ClusterRole
name: kube-keepalived-vip
subjects:
- kind: ServiceAccount
name: kube-keepalived-vip
namespace: defaultclusterrolebinding.yaml
apiVersion: rbac.authorization.k8s.io/v1alpha1
kind: ClusterRoleBinding
metadata:
name: kube-keepalived-vip
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: ClusterRole
name: kube-keepalived-vip
subjects:
- kind: ServiceAccount
name: kube-keepalived-vip
namespace: default$ kubectl create -f vip-rbac.yaml
$ kubectl create -f clusterrolebinding.yaml先建立一个简单的 service
nginx-deployment.yaml
apiVersion: apps/v1beta1
kind: Deployment
metadata:
name: nginx-deployment
spec:
replicas: 3
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:1.7.9
ports:
- containerPort: 80
---
apiVersion: v1
kind: Service
metadata:
name: nginx
labels:
app: nginx
spec:
type: NodePort
ports:
- port: 80
nodePort: 30302
targetPort: 80
protocol: TCP
name: http
selector:
app: nginx主要功能就是 pod 去监听听 80 port, 再开启 service NodePort 监听 30320
$ kubecrl create -f nginx-deployment.yaml接下来我们要做的是 config map
$ echo "apiVersion: v1
kind: ConfigMap
metadata:
name: vip-configmap
data:
10.87.2.50: default/nginx" | kubectl create -f -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
$kubectl get configmap
NAME DATA AGE
vip-configmap 1 23h
再来就是设置 keepalived-vip
apiVersion: extensions/v1beta1
kind: DaemonSet
metadata:
name: kube-keepalived-vip
spec:
template:
metadata:
labels:
name: kube-keepalived-vip
spec:
hostNetwork: true
containers:
- image: gcr.io/google_containers/kube-keepalived-vip:0.9
name: kube-keepalived-vip
imagePullPolicy: Always
securityContext:
privileged: true
volumeMounts:
- mountPath: /lib/modules
name: modules
readOnly: true
- mountPath: /dev
name: dev
# use downward API
env:
- name: POD_NAME
valueFrom:
fieldRef:
fieldPath: metadata.name
- name: POD_NAMESPACE
valueFrom:
fieldRef:
fieldPath: metadata.namespace
# to use unicast
args:
- --services-configmap=default/vip-configmap
# unicast uses the ip of the nodes instead of multicast
# this is useful if running in cloud providers (like AWS)
#- --use-unicast=true
volumes:
- name: modules
hostPath:
path: /lib/modules
- name: dev
hostPath:
path: /dev建立 daemonset
$ kubectl get daemonset kube-keepalived-vip
NAME DESIRED CURRENT READY UP-TO-DATE AVAILABLE NODE-SELECTOR AGE
kube-keepalived-vip 5 5 5 5 5检查一下配置状态
kubectl get pod -o wide |grep keepalive
kube-keepalived-vip-c4sxw 1/1 Running 0 23h 10.87.2.6 10.87.2.6
kube-keepalived-vip-c9p7n 1/1 Running 0 23h 10.87.2.8 10.87.2.8
kube-keepalived-vip-psdp9 1/1 Running 0 23h 10.87.2.10 10.87.2.10
kube-keepalived-vip-xfmxg 1/1 Running 0 23h 10.87.2.12 10.87.2.12
kube-keepalived-vip-zjts7 1/1 Running 3 23h 10.87.2.4 10.87.2.4可以随机挑一个 pod, 去看里面的配置
$ kubectl exec kube-keepalived-vip-c4sxw cat /etc/keepalived/keepalived.conf
global_defs {
vrrp_version 3
vrrp_iptables KUBE-KEEPALIVED-VIP
}
vrrp_instance vips {
state BACKUP
interface eno1
virtual_router_id 50
priority 103
nopreempt
advert_int 1
track_interface {
eno1
}
virtual_ipaddress {
10.87.2.50
}
}
# Service: default/nginx
virtual_server 10.87.2.50 80 { // 此为 service 开的口
delay_loop 5
lvs_sched wlc
lvs_method NAT
persistence_timeout 1800
protocol TCP
real_server 10.2.49.30 8080 { // 这里说明 pod 的真实状况
weight 1
TCP_CHECK {
connect_port 80
connect_timeout 3
}
}
}
最后我们去测试这功能
$ curl 10.87.2.50
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
body {
width: 35em;
margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif;
}
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>
<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>
<p><em>Thank you for using nginx.</em></p>
</body>
</html>
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。