@Service DNS
CoreDNS服务为每一个Service创建DNS记录用于域名解析
ClusterIP记录格式：<service-name>.<namespace-name>.svc.cluster.local
[root@k8s-master ~]# kubectl get pod -n kube-system| grep dns
coredns-7f89b7bc75-mgtnj 1/1 Running 24 34d
coredns-7f89b7bc75-wkrjq 1/1 Running 24 34d
[root@k8s-master ~]# kubectl exec -it coredns-7f89b7bc75-mgtnj -n kube-system -- bash
OCI runtime exec failed: exec failed: container_linux.go:380: starting container process caused: exec: "bash": executable file not found in $PATH: unknown
command terminated with exit code 126
[root@k8s-master ~]# kubectl exec -it coredns-7f89b7bc75-mgtnj -n kube-system -- sh
OCI runtime exec failed: exec failed: container_linux.go:380: starting container process caused: exec: "sh": executable file not found in $PATH: unknown
command terminated with exit code 126
[root@k8s-master ~]#由于coredns pod进不去bash，部署一个busybox看看
[root@k8s-master ~]# kubectl run dns --image=busybox:1.28.4 -- sleep 3600
pod/dns created
[root@k8s-master ~]#默认命名空间有一个kubernetes,用nslookup试试
[root@k8s-master ~]# kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 34d
[root@k8s-master ~]#
[root@k8s-master ~]# kubectl get pod
NAME READY STATUS RESTARTS AGE
dns 1/1 Running 0 65s
nfs-client-provisioner-5fd446cd9d-c62kl 1/1 Running 0 5h10m
[root@k8s-master ~]#
[root@k8s-master ~]# kubectl exec -it dns -- sh
/ # nslookup kubernetes
Server: 10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local
Name: kubernetes
Address 1: 10.96.0.1 kubernetes.default.svc.cluster.local
/ # exit
[root@k8s-master ~]#再看看命名空间kube-system,发现如果不加命名空间找不到,这个格式越完整搜索范围越小
[root@k8s-master ~]# kubectl get svc -n kube-system
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kube-dns ClusterIP 10.96.0.10 <none> 53/UDP,53/TCP,9153/TCP 34d
metrics-server ClusterIP 10.96.228.107 <none> 443/TCP 34d
[root@k8s-master ~]#
[root@k8s-master ~]# kubectl exec -it dns -- sh
/ # nslookup kube-dns
Server: 10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local
nslookup: can't resolve 'kube-dns'
/ # nslookup metrics-server
Server: 10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local
nslookup: can't resolve 'metrics-server'
/ # 加上命名空间 或者 搜索ClusterIP就能找到
/ # nslookup kube-dns.kube-system
Server: 10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local
Name: kube-dns.kube-system
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local
/ #
/ # nslookup metrics-server.kube-system
Server: 10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local
Name: metrics-server.kube-system
Address 1: 10.96.228.107 metrics-server.kube-system.svc.cluster.local
/ #@ StatefulSet控制器
Deployment中Pod是平等的,StatefulSet中的Pod不等价且有序(例如mysql的读写分离)，所以
- StatefulSet不通过ClusterIP访问，使用无头服务(Headless Service)
- StatefulSet的存储卷使用卷申领模板(VolumeClaimTemplate)创建，和PVC类似，但是会为每个Pod创建一个PVC并分配编号
可以参考官网的yaml ->
https://kubernetes.io/zh/docs/tutorials/stateful-application/basic-stateful-set/
test-statefulset.yaml 内容如下,
apiVersion: v1
kind: Service
metadata:
name: web-stat
labels:
app: test-statefulset
spec:
ports:
- port: 80
name: web-stat
clusterIP: None
selector:
app: test-statefulset
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: web
spec:
serviceName: "web-stat"
replicas: 3
selector:
matchLabels:
app: test-statefulset
template:
metadata:
labels:
app: test-statefulset
spec:
containers:
- name: web-stat
image: nginx
ports:
- containerPort: 80
name: web-stat
volumeMounts:
- name: www
mountPath: /usr/share/nginx/html
volumeClaimTemplates:
- metadata:
name: www
spec:
storageClassName: "managed-nfs-storage"
accessModes: [ "ReadWriteOnce" ]
resources:
requests:
storage: 1Gi说明：
line 11 资源SVC,clusterIP: None,不分配clusterIP使用无头服务
line 20 资源StatefulSet的serviceName: "web-stat"和资源SVC的name: web-stat(line 4)要对应
line 43 volumeClaimTemplates中定义存储使用动态共给storageClassName: "managed-nfs-storage"
创建Service, StatefulSet, 可以观察到 (1) Pod是有序起来的,Pod名称后有一个编号
[root@k8s-master ~]# kubectl apply -f test-statefulset.yaml
service/web-stat created
statefulset.apps/web created
[root@k8s-master ~]# kubectl get pod
NAME READY STATUS RESTARTS AGE
dns 1/1 Running 0 57m
nfs-client-provisioner-5fd446cd9d-c62kl 1/1 Running 0 6h7m
web-0 1/1 Running 0 31s
web-1 0/1 ContainerCreating 0 12s
[root@k8s-master ~]# kubectl get pod
NAME READY STATUS RESTARTS AGE
dns 1/1 Running 0 57m
nfs-client-provisioner-5fd446cd9d-c62kl 1/1 Running 0 6h7m
web-0 1/1 Running 0 40s
web-1 1/1 Running 0 21s
web-2 0/1 Pending 0 1s
[root@k8s-master ~]# kubectl get pod
NAME READY STATUS RESTARTS AGE
dns 1/1 Running 0 57m
nfs-client-provisioner-5fd446cd9d-c62kl 1/1 Running 0 6h7m
web-0 1/1 Running 0 47s
web-1 1/1 Running 0 28s
web-2 1/1 Running 0 8s
[root@k8s-master ~]#(2) 所创建的SVC的的ClusterIP为None
[root@k8s-master ~]# kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 34d
web-stat ClusterIP None <none> 80/TCP 109s
[root@k8s-master ~]#(3) nslookup这个无头服务,解析的是三个Pod的地址; 而()Deployment部署解析的是ClusterIP
StaetefulSet:
[root@k8s-master ~]# kubectl exec -it dns -- sh
/ # nslookup web
Server: 10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local
nslookup: can't resolve 'web'
/ # nslookup web-stat
Server: 10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local
Name: web-stat
Address 1: 10.244.36.96 web-0.web-stat.default.svc.cluster.local
Address 2: 10.244.169.154 web-2.web-stat.default.svc.cluster.local
Address 3: 10.244.36.91 web-1.web-stat.default.svc.cluster.local
/ #
-----------
Deployment:
[root@k8s-master ~]# kubectl apply -f test-deploy-svc.yaml
deployment.apps/de-web created
service/de-web created
[root@k8s-master ~]# kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
de-web NodePort 10.111.52.13 <none> 80:30006/TCP 65s
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 34d
web-stat ClusterIP None <none> 80/TCP 16m
[root@k8s-master ~]# kubectl get ep
NAME ENDPOINTS AGE
de-web 10.244.169.151:80,10.244.36.100:80,10.244.36.98:80 68s
k8s-sigs.io-nfs-subdir-external-provisioner <none> 6h22m
kubernetes 192.168.231.121:6443 34d
web-stat 10.244.169.154:80,10.244.36.91:80,10.244.36.96:80 16m
[root@k8s-master ~]#
[root@k8s-master ~]# kubectl exec -it dns -- sh
/ # nslookup de-web
Server: 10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local
Name: de-web
Address 1: 10.111.52.13 de-web.default.svc.cluster.local
/ # exit
[root@k8s-master ~]#
Service ClusterIP记录格式：<service-name>.<namespace-name>.svc.cluster.local
无头服务地址记录格式: <pod-name>.<service-name>.<namespace-name>.svc.cluster.local
(4) 三个Pod对应三个PVC, 各自绑定一个PV, 存储互不干扰
[root@k8s-master ~]# kubectl get pvc
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
www-web-0 Bound pvc-d300aaa3-b98c-4d16-9bc5-76b4df012a67 1Gi RWO managed-nfs-storage 2m14s
www-web-1 Bound pvc-b8035a5d-8ce7-4b11-b253-d97c1f8dc8d9 1Gi RWO managed-nfs-storage 115s
www-web-2 Bound pvc-c129ccb2-69d2-468f-b98f-74ce490b9822 1Gi RWO managed-nfs-storage 95s
[root@k8s-master ~]#
[root@k8s-master ~]# kubectl get pv
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
pvc-b8035a5d-8ce7-4b11-b253-d97c1f8dc8d9 1Gi RWO Delete Bound default/www-web-1 managed-nfs-storage 119s
pvc-c129ccb2-69d2-468f-b98f-74ce490b9822 1Gi RWO Delete Bound default/www-web-2 managed-nfs-storage 99s
pvc-d300aaa3-b98c-4d16-9bc5-76b4df012a67 1Gi RWO Delete Bound default/www-web-0 managed-nfs-storage 2m18s
[root@k8s-master ~]#
NFS:
[root@k8s-node2 nfstest]# ls -l
total 0
drwxrwxrwx 2 root root 22 Aug 29 12:07 archived-default-test-sc-pvc-7b7c6f87-95e2-4d58-97af-b06723154615
drwxrwxrwx 2 root root 6 Aug 29 17:07 default-www-web-0-pvc-d300aaa3-b98c-4d16-9bc5-76b4df012a67
drwxrwxrwx 2 root root 6 Aug 29 17:07 default-www-web-1-pvc-b8035a5d-8ce7-4b11-b253-d97c1f8dc8d9
drwxrwxrwx 2 root root 6 Aug 29 17:07 default-www-web-2-pvc-c129ccb2-69d2-468f-b98f-74ce490b9822
[root@k8s-node2 nfstest]#