在分布式微服务的访问中，我们在有可能的情况下需要互相调用各个模块的应用接口，这个时候就需要对对方的IP进行识别，我们称之为服务发现。在k8s中，Service提供了集群内部的虚拟IP，供集群内部的容器访问。
# kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.10.10.1 <none> 443/TCP 6d
my-service ClusterIP 10.10.10.150 <none> 80/TCP,443/TCP 2d
其中my-service服务对应的集群IP则为10.10.10.150
首先看一下node的标签
# kubectl get node --show-labels
NAME STATUS ROLES AGE VERSION LABELS
172.18.98.46 Ready <none> 5d v1.9.2 beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,kubernetes.io/hostname=172.18.98.46
172.18.98.47 Ready <none> 5d v1.9.2 beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,env_role=dev,kubernetes.io/hostname=172.18.98.47
其中172.18.98.47有一个env_role=dev的标签
我们起一个pod，pod的yaml配置如下
# cat pod.yaml
apiVersion: v1
kind: Pod
metadata:
name: nginx-pod
labels:
app: nginx-pod
spec:
#nodeName: 172.18.98.47
nodeSelector:
env_role: dev
containers:
- name: nginx
image: nginx:1.13
ports:
- containerPort: 80
livenessProbe:
httpGet:
path: /index.html
port: 80
resources:
requests:
memory: "64Mi"
cpu: "250m"
limits:
memory: "128Mi"
cpu: "500m"
restartPolicy: OnFailure
它会固定被分配到env_role: dev的node上。
# kubectl create -f pod.yaml
pod "nginx-pod" created
我们通过查看my-service的内容可知，该服务的选择器为该pod
# kubectl describe svc my-service
Name: my-service
Namespace: default
Labels: <none>
Annotations: <none>
Selector: app=nginx-pod
Type: ClusterIP
IP: 10.10.10.150
Port: http 80/TCP
TargetPort: 80/TCP
Endpoints: 172.17.94.6:80
Port: https 443/TCP
TargetPort: 443/TCP
Endpoints: 172.17.94.6:443
Session Affinity: None
Events: <none>
查看k8s集群的endpoints
# kubectl get ep
NAME ENDPOINTS AGE
kubernetes 172.18.98.48:6443 6d
my-service 172.17.94.6:80,172.17.94.6:443 2d
查看该pod的IP
# kubectl get pod -o wide | grep nginx-pod
nginx-pod 1/1 Running 0 41m 172.17.94.6 172.18.98.47
刚好为172.17.94.6
现在进行DNS的yaml文件的配置
vim kube-dns.yaml
内容如下
apiVersion: v1
kind: Service
metadata:
name: kube-dns
namespace: kube-system
labels:
k8s-app: kube-dns
kubernetes.io/cluster-service: "true"
addonmanager.kubernetes.io/mode: Reconcile
kubernetes.io/name: "kubeDNS"
spec:
selector:
k8s-app: kube-dns
clusterIP: 10.10.10.2
ports:
- name: dns
port: 53
protocol: UDP
- name: dns-tcp
port: 53
protocol: TCP
---
apiVersion: v1
kind: ServiceAccount
metadata:
name: kube-dns
namespace: kube-system
labels:
kubernetes.io/cluster-service: "true"
addonmanager.kubernetes.io/mode: Reconcile
---
apiVersion: v1
kind: ConfigMap
metadata:
name: kube-dns
namespace: kube-system
labels:
addonmanager.kubernetes.io/mode: EnsureExists
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: kube-dns
namespace: kube-system
labels:
k8s-app: kube-dns
kubernetes.io/cluster-service: "true"
addonmanager.kubernetes.io/mode: Reconcile
spec:
strategy:
rollingUpdate:
maxSurge: 10%
maxUnavailable: 0
selector:
matchLabels:
k8s-app: kube-dns
template:
metadata:
labels:
k8s-app: kube-dns
annotations:
scheduler.alpha.kubernetes.io/critical-pod: ''
spec:
tolerations:
- key: "CriticalAddonsOnly"
operator: "Exists"
volumes:
- name: kube-dns-config
configMap:
name: kube-dns
optional: true
containers:
- name: kubedns
image: registry.cn-hangzhou.aliyuncs.com/google_containers/k8s-dns-kube-dns-amd64:1.14.7
resources:
limits:
memory: 170Mi
requests:
cpu: 100m
memory: 70Mi
# livenessProbe:
# httpGet:
# path: /healthcheck/kubedns
# port: 10054
# scheme: HTTP
# initialDelaySeconds: 60
# timeoutSeconds: 5
# successThreshold: 1
# failureThreshold: 5
# readinessProbe:
# httpGet:
# path: /readiness
# port: 8081
# scheme: HTTP
# initialDelaySeconds: 3
# timeoutSeconds: 5
args:
- --domain=cluster.local.
- --dns-port=10053
- --config-dir=/kube-dns-config
- --v=2
env:
- name: PROMETHEUS_PORT
value: "10055"
ports:
- containerPort: 10053
name: dns-local
protocol: UDP
- containerPort: 10053
name: dns-tcp-local
protocol: TCP
- containerPort: 10055
name: metrics
protocol: TCP
volumeMounts:
- name: kube-dns-config
mountPath: /kube-dns-config
- name: dnsmasq
image: registry.cn-hangzhou.aliyuncs.com/google_containers/k8s-dns-dnsmasq-nanny-amd64:1.14.7
# livenessProbe:
# httpGet:
# path: /healthcheck/dnsmasq
# port: 10054
# scheme: HTTP
# initialDelaySeconds: 60
# timeoutSeconds: 5
# successThreshold: 1
# failureThreshold: 5
args:
- -v=2
- -logtostderr
- -configDir=/etc/k8s/dns/dnsmasq-nanny
- -restartDnsmasq=true
- --
- -k
- --cache-size=1000
- --no-negcache
- --log-facility=-
- --server=/cluster.local/127.0.0.1#10053
- --server=/in-addr.arpa/127.0.0.1#10053
- --server=/ip6.arpa/127.0.0.1#10053
ports:
- containerPort: 53
name: dns
protocol: UDP
- containerPort: 53
name: dns-tcp
protocol: TCP
resources:
requests:
cpu: 150m
memory: 20Mi
volumeMounts:
- name: kube-dns-config
mountPath: /etc/k8s/dns/dnsmasq-nanny
- name: sidecar
image: registry.cn-hangzhou.aliyuncs.com/google_containers/k8s-dns-sidecar-amd64:1.14.7
livenessProbe:
httpGet:
path: /metrics
port: 10054
scheme: HTTP
initialDelaySeconds: 60
timeoutSeconds: 5
successThreshold: 1
failureThreshold: 5
args:
- --v=2
- --logtostderr
- --probe=kubedns,127.0.0.1:10053,kubernetes.default.svc.cluster.local,5,SRV
- --probe=dnsmasq,127.0.0.1:53,kubernetes.default.svc.cluster.local,5,SRV
ports:
- containerPort: 10054
name: metrics
protocol: TCP
resources:
requests:
memory: 20Mi
cpu: 10m
dnsPolicy: Default
serviceAccountName: kube-dns
我把其中一些健康检查给注释掉了，启动该文件
# kubectl create -f kube-dns.yaml
查看kube-system命名空间的信息
# kubectl get all -n kube-system
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
deploy/kube-dns 1 1 1 1 4h
NAME DESIRED CURRENT READY AGE
rs/kube-dns-769d6c4665 1 1 1 4h
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
deploy/kube-dns 1 1 1 1 4h
NAME DESIRED CURRENT READY AGE
rs/kube-dns-769d6c4665 1 1 1 4h
NAME READY STATUS RESTARTS AGE
po/kube-dns-769d6c4665-ph7dm 3/3 Running 0 4h
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
svc/kube-dns ClusterIP 10.10.10.2 <none> 53/UDP,53/TCP 4h
可以看到dns的配置启动成功。
验证该dns
我们启动一个busybox的pod,yaml配置如下
vim busybox.yaml
apiVersion: v1
kind: Pod
metadata:
name: busybox
namespace: default
spec:
containers:
- image: busybox:1.24
command:
- sleep
- "3600"
imagePullPolicy: IfNotPresent
name: busybox
restartPolicy: Always
运行该pod
kubectl create -f busybox.yaml
# kubectl exec -it busybox -- nslookup kubernetes.default
Server: 10.10.10.2
Address 1: 10.10.10.2 kube-dns.kube-system.svc.cluster.local
Name: kubernetes.default
Address 1: 10.10.10.1 kubernetes.default.svc.cluster.local
# kubectl exec -it busybox -- nslookup my-service.default
Server: 10.10.10.2
Address 1: 10.10.10.2 kube-dns.kube-system.svc.cluster.local
Name: my-service.default
Address 1: 10.10.10.150 my-service.default.svc.cluster.local
我们可以看到my-service的k8s集群虚拟IP被解析出来了，为10.10.10.150
来源：oschina
链接：https://my.oschina.net/u/3768341/blog/3015013