参考https://blog.csdn.net/qq_25611295/article/details/84238940
https://blog.51cto.com/ylw6006/2108426
接我之前搭建的k8s的文章
一、构建coredns服务
将下载的 kubernetes-server-linux-amd64.tar.gz 解压后，再解压其中的 kubernetes-src.tar.gz 文件。coredns 对应的目录是：cluster/addons/dns。
cd /opt/test/kubernetes/cluster/addons/dns/coredns
将coredns模板复制出来：
cp coredns.yaml.base coredns.yaml
修改一些参数：
修改参数有3个地方，一个是ip6.arpa 指定，一个是更改成国内镜像源，一个是定义clusterIP，具体如下
ip6.arpa修改为kubernetes cluster.local. in-addr.arpa ip6.arpa
国内镜像修改为 coredns/coredns:1.2.6
clusterIP修改为自己集群设置的IP范围内的，我集群的是 10.10.10.0/24,所以设置为10.10.10.2（且不为已使用的IP）
具体的yaml是(我们只需修改clusterIP的IP为自己集群的IP范围内，且不重复的)
apiVersion: v1
kind: ServiceAccount
metadata:
name: coredns
namespace: kube-system
labels:
kubernetes.io/cluster-service: "true"
addonmanager.kubernetes.io/mode: Reconcile
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
labels:
kubernetes.io/bootstrapping: rbac-defaults
addonmanager.kubernetes.io/mode: Reconcile
name: system:coredns
rules:
- apiGroups:
- ""
resources:
- endpoints
- services
- pods
- namespaces
verbs:
- list
- watch
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
annotations:
rbac.authorization.kubernetes.io/autoupdate: "true"
labels:
kubernetes.io/bootstrapping: rbac-defaults
addonmanager.kubernetes.io/mode: EnsureExists
name: system:coredns
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: ClusterRole
name: system:coredns
subjects:
- kind: ServiceAccount
name: coredns
namespace: kube-system
---
apiVersion: v1
kind: ConfigMap
metadata:
name: coredns
namespace: kube-system
labels:
addonmanager.kubernetes.io/mode: EnsureExists
data:
Corefile: |
.:53 {
errors
health
kubernetes cluster.local. in-addr.arpa ip6.arpa {
pods insecure
upstream
fallthrough in-addr.arpa ip6.arpa
}
prometheus :9153
proxy . /etc/resolv.conf
cache 30
loop
reload
loadbalance
}
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: coredns
namespace: kube-system
labels:
k8s-app: kube-dns
kubernetes.io/cluster-service: "true"
addonmanager.kubernetes.io/mode: Reconcile
kubernetes.io/name: "CoreDNS"
spec:
# replicas: not specified here:
# 1. In order to make Addon Manager do not reconcile this replicas parameter.
# 2. Default is 1.
# 3. Will be tuned in real time if DNS horizontal auto-scaling is turned on.
strategy:
type: RollingUpdate
rollingUpdate:
maxUnavailable: 1
selector:
matchLabels:
k8s-app: kube-dns
template:
metadata:
labels:
k8s-app: kube-dns
annotations:
seccomp.security.alpha.kubernetes.io/pod: 'docker/default'
spec:
serviceAccountName: coredns
tolerations:
- key: node-role.kubernetes.io/master
effect: NoSchedule
- key: "CriticalAddonsOnly"
operator: "Exists"
containers:
- name: coredns
image: coredns/coredns:1.2.6
imagePullPolicy: IfNotPresent
resources:
limits:
memory: 170Mi
requests:
cpu: 100m
memory: 70Mi
args: [ "-conf", "/etc/coredns/Corefile" ]
volumeMounts:
- name: config-volume
mountPath: /etc/coredns
readOnly: true
ports:
- containerPort: 53
name: dns
protocol: UDP
- containerPort: 53
name: dns-tcp
protocol: TCP
- containerPort: 9153
name: metrics
protocol: TCP
livenessProbe:
httpGet:
path: /health
port: 8080
scheme: HTTP
initialDelaySeconds: 60
timeoutSeconds: 5
successThreshold: 1
failureThreshold: 5
securityContext:
allowPrivilegeEscalation: false
capabilities:
add:
- NET_BIND_SERVICE
drop:
- all
readOnlyRootFilesystem: true
dnsPolicy: Default
volumes:
- name: config-volume
configMap:
name: coredns
items:
- key: Corefile
path: Corefile
---
apiVersion: v1
kind: Service
metadata:
name: kube-dns
namespace: kube-system
annotations:
prometheus.io/port: "9153"
prometheus.io/scrape: "true"
labels:
k8s-app: kube-dns
kubernetes.io/cluster-service: "true"
addonmanager.kubernetes.io/mode: Reconcile
kubernetes.io/name: "CoreDNS"
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
创建dns:
kubectl create -f coredns.yaml
检查pod和svc的情况：
[root@K8S-M1 ~]# kubectl get all -n kube-system
NAME READY STATUS RESTARTS AGE
pod/coredns-57b8565df8-nnpcc 1/1 Running 1 9h
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kube-dns ClusterIP 10.10.10.2 53/UDP,53/TCP 9h
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
deployment.apps/coredns 1 1 1 1 9h
NAME DESIRED CURRENT READY AGE
replicaset.apps/coredns-57b8565df8 1 1 1 9h
检查coreDNS服务，这里已经启动
[root@K8S-M1 ~]# kubectl cluster-info
Kubernetes master is running at http://localhost:8080
CoreDNS is running at http://localhost:8080/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
二、测试：
创建一个简单的centos,busybox有点坑，测试有问题。
[root@master yml_files]# cat centos.yaml
apiVersion: v1
kind: Pod
metadata:
name: centoschao
namespace: default
spec:
containers:
- image: centos
command:
- sleep
- "3600"
imagePullPolicy: IfNotPresent
name: centoschao
restartPolicy: Always
创建：
kubectl create -f centos.yaml
验证
[root@K8S-M1 ~]# kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.10.10.1 443/TCP 15d
nginx ClusterIP 10.10.10.252 80/TCP 9h
[root@K8S-M1 ~]# kubectl exec -it centoschao sh
sh-4.2# yum install bind-utils -y
sh-4.2# nslookup kubernetes
Server: 10.10.10.2
Address: 10.10.10.2#53
Name: kubernetes.default.svc.cluster.local
Address: 10.10.10.1
sh-4.2# nslookup nginx
Server: 10.10.10.2
Address: 10.10.10.2#53
Name: nginx.default.svc.cluster.local
Address: 10.10.10.252
sh-4.2# nslookup nginx.default.svc.cluster.local
Server: 10.10.10.2
Address: 10.10.10.2#53
Name: nginx.default.svc.cluster.local
Address: 10.10.10.252
ok,成功了
说一下busybox，很坑，我之前安装coredns时，使用busybox测试，发现会出现问题，我还以为是安装失败，检查了许久，浪费时间精力
看一下，它是如何坑的
[root@K8S-M1 ~]$ kubectl run -i --tty busybox --image=docker.io/busybox /bin/sh
/ # nslookup nginx
Server: 10.10.10.2
Address: 10.10.10.2#53
** server can't find my-nginx: NXDOMAIN