k8s_centos7 安装部署coredns

1.简单来说，服务发现橘色服务（应用）之间相互定位的过程

2.服务发现并非云主机时代独有，传统的单体架构时代也会用到。以下应用场景下，更需要服务发现：
服务（应用）的动态性强
服务（应用）更新发布频繁
服务（应用）支持自动伸缩

3.在K8S集群里，POD的IP不断变化的，如何“以不变应万变”呢
抽象出了Service资源，通过标签选择器，关联一组pod
抽象出了集群网络，通过相对固定的“集群IP”，使服务接入点固定

4.如何自动关联Service资源的“名称”和“集群网络IP”，从而达到服务被集群自动发现的目的呢
传统的DNS模型：hdss7-14.host.com -> 192.168.16.14
能否在k8s里建立这样的模型：nginx-ds -> 10.254.0.5

5.K8S里服务发现的方式 - DNS

6.实现K8S里DNS功能的插件（软件）
kube-dns-kuberbetes-v1.2至kuberbetes-v1.10
Coredns-kuberbetes-v1.11至今

注意：
K8S里的DNS不是万能的！它应该只负责自动维护“服务名” -> “集群网络IP”之间的关系

---

K8S的服务发现插件 - CoreDNS
部署K8S的内网资源配置清单http服务

在运维主机HDSS7-12.host.com上，配置一个nginx虚拟主机，用以提供K8S统一的资源配置清单访问入口

配置nginx
[[email protected] ~]# mkdir /data/k8s-yaml
[[email protected] ~]# vi /etc/nginx/conf.d/k8s-yaml.od.com.conf
server {
listen 80;
server_name k8s-yaml.od.com;

location / {
    autoindex on;
    default_type text/plain;
    root /data/k8s-yaml;
}

}
[[email protected] ~]# nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

[[email protected] ~]# nginx -s reload

---

配置内网DNS解析
[[email protected] ~]# vi /var/named/od.com.zone
$ORIGIN od.com.
$TTL 600 ; 10 minutes
@ IN SOA dns.od.com. dnsadmin.od.com. (
2019120903 ; serial # 03，***做下前滚
10800 ; refresh (3 hours)
900 ; retry (15 minutes)
604800 ; expire (1 week)
86400 ; minimum (1 day)
)
NS dns.od.com.
$TTL 60 ; 1 minute
dns A 192.168.16.11
harbor A 192.168.16.12
k8s-yaml A 192.168.16.12 # 添加地址解析

[[email protected] ~]# systemctl restart named

[[email protected] ~]# dig -t A k8s-yaml.od.com @192.168.16.11 +short

---

[[email protected] ~]# cd /data/k8s-yaml/
[[email protected] k8s-yaml]# mkdir coredns

---

制作上传coredns的镜像
[[email protected] k8s-yaml]# docker pull coredns/coredns:1.6.1
[[email protected] k8s-yaml]# docker tag coredns/coredns:1.6.1 harbor.od.com/public/coredns:v1.6.1
[[email protected] k8s-yaml]# docker push harbor.od.com/public/coredns:v1.6.1

创建资源管理配置清单
[[email protected] k8s-yaml]# cd coredns/

[[email protected] coredns]# vi rbac.yaml
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

[[email protected] coredns]# vi cm.yaml
apiVersion: v1
kind: ConfigMap
metadata:
name: coredns
namespace: kube-system
data:
Corefile: |
.:53 {
errors
log
health
ready
kubernetes cluster.local 10.254.0.0/16 # service网段
forward . 192.168.16.11 # 物理机安装dns服务的地址
cache 30
loop
reload
loadbalance
}

[[email protected] coredns]# vi dp.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: coredns
namespace: kube-system
labels:
k8s-app: coredns
kubernetes.io/name: “CoreDNS”
spec:
replicas: 1
selector:
matchLabels:
k8s-app: coredns
template:
metadata:
labels:
k8s-app: coredns
spec:
priorityClassName: system-cluster-critical
serviceAccountName: coredns
containers:
- name: coredns
image: harbor.od.com/public/coredns:v1.6.1
args:
- -conf
- /etc/coredns/Corefile
volumeMounts:
- name: config-volume
mountPath: /etc/coredns
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
dnsPolicy: Default
volumes:
- name: config-volume
configMap:
name: coredns
items:
- key: Corefile
path: Corefile

[[email protected] coredns]# vi svc.yaml
apiVersion: v1
kind: Service
metadata:
name: coredns
namespace: kube-system
labels:
k8s-app: coredns
kubernetes.io/cluster-service: “true”
kubernetes.io/name: “CoreDNS”
spec:
selector:
k8s-app: coredns
clusterIP: 10.254.0.2 # dns服务的ip
ports:

• name: dns
  port: 53
  protocol: UDP
• name: dns-tcp
  port: 53
• name: metrics
  port: 9153
  protocol: TCP

官方coredns资源配置清单下载地址
https://github.com/kubernetes/kubernetes/blob/master/cluster/addons/dns/coredns/coredns.yaml.base

---

在mater上运行
[[email protected] ~]# kubectl apply -f http://k8s-yaml.od.com/coredns/rbac.yaml
[[email protected] ~]# kubectl apply -f http://k8s-yaml.od.com/coredns/cm.yaml
[[email protected] ~]# kubectl apply -f http://k8s-yaml.od.com/coredns/dp.yaml
[[email protected] ~]# kubectl apply -f http://k8s-yaml.od.com/coredns/svc.yaml

[[email protected] ~]# kubectl get svc -n kube-system
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
coredns ClusterIP 10.254.0.2 53/UDP,53/TCP,9153/TCP 26s

[[email protected] ~]# kubectl get all -n kube-system
NAME READY STATUS RESTARTS AGE
pod/coredns-6b6c4f9648-srsht 1/1 Running 0 114s

NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/coredns ClusterIP 10.254.0.2 53/UDP,53/TCP,9153/TCP 101s

NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/coredns 1/1 1 1 114s

NAME DESIRED CURRENT READY AGE
replicaset.apps/coredns-6b6c4f9648 1 1 1 114s

---

[[email protected] bin]# cat kubelet.sh # 里面定义了dns的ip地址

---

验证dns服务
[[email protected] ~]# dig -t A www.baidu.com @10.254.0.2 +short
www.a.shifen.com.
180.101.49.12
180.101.49.11
[[email protected] ~]# dig -t A hdss7-11.host.com @10.254.0.2 +short
192.168.16.11

---

[[email protected] ~]# kubectl create deployment nginx-dp --image=harbor.od.com/public/nginx:v1.7.9 -n kube-public

[[email protected] ~]# kubectl expose deployment nginx-dp --port=80 -n kube-public

[[email protected] ~]# dig -t A nginx-dp.kube-public.svc.cluster.local. @10.254.0.2 +short
10.254.127.91

[[email protected] ~]# kubectl get pod -n kube-public
NAME READY STATUS RESTARTS AGE
nginx-dp-5dfc689474-xzfgq 1/1 Running 0 6m57s

[[email protected] ~]# kubectl exec -it nginx-dp-5dfc689474-xzfgq /bin/bash -n kube-public

[email protected]:/# cat /etc/resolv.conf
nameserver 10.254.0.2
search kube-public.svc.cluster.local svc.cluster.local cluster.local host.com
options ndots:5

CoreDNS：Kubernetes内部域名解析原理、弊端及优化方式
http://ccnuo.com/