kubernetes基础入门之-配置kubernetes skyDNS服务
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部署kubernetes skyDNS
kubernetes可以为pod提供dns内部域名解析服务。
其主要作用是为pod提供可以直接通过service的名字解析为对应service的ip的功能！
1.首先在各节点的kubelet 进程中添加选项：
KUBELET_ARGS="--cluster_dns=10.254.0.10 --cluster_domain=kube.local"
【Master 节点操作如下:】
# cat dns/kubedns-rc.yaml
kind: ReplicationController
metadata:
name: kube-dns-v6
namespace: default
labels:
k8s-app: kube-dns
version: v6
kubernetes.io/cluster-service: "true"
spec:
replicas: 1
version: v6
template:
metadata:
labels:
k8s-app: kube-dns
version: v6
kubernetes.io/cluster-service: "true"
spec:
containers:
- name: etcd
image: index.tenxcloud.com/google_containers/etcd:2.0.9
command:
- /usr/local/bin/etcd
- -listen-client-urls
- http://0.0.0.0:2379,http://0.0.0.0:4001
- -advertise-client-urls
- http://127.0.0.1:2379,http://127.0.0.1:4001
- name: kube2sky
image: index.tenxcloud.com/google_containers/kube2sky:1.11
resources:
limits:
cpu: 100m
memory: 50Mi
command:
- /kube2sky
- --kube_master_url=http://192.168.11.10:8080
- -domain=kube.local
- name: skydns
image: index.tenxcloud.com/google_containers/skydns:2015-03-11-001
resources:
command:
- /skydns
- -machines=http://localhost:4001
- -addr=0.0.0.0:53
- -domain=kube.local
ports:
- containerPort: 53
name: dns
protocol: UDP
- containerPort: 53
name: dns-tcp
protocol: TCP
dnsPolicy: Default
# cat dns/kubedns-service.yaml
apiVersion: v1
kind: Service
metadata:
name: kube-dns
namespace: default
labels:
k8s-app: kube-dns
kubernetes.io/cluster-service: "true"
kubernetes.io/name: "KubeDNS"
spec:
selector:
k8s-app: kube-dns
clusterIP: 10.254.0.10
ports:
- name: dns
port: 53
protocol: UDP
- name: dns-tcp
port: 53
protocol: TCP
注意：
(pause负责管理pod的网络等相关事务: gcr.io/google_containers/pause-amd64:3.0)
谷歌被墙了，可以通过以下方式来使用：
1.***或访问国内的docker镜像站点,下载下来改名
# docker pull mritd/pause-amd64:3.0
# docker tag mritd/pause-amd64:3.0 gcr.io/google_containers/pause-amd64:3.0
2.使用内部私有仓库,在各k8s节点的kubelet 服务进程添加下面参数：
"--pod-infra-container-image=my.hub.io/pause-amd64:3.0"
>>> node 节点镜像列表 [实际环境中建议使用私有仓库的镜像]：
# docker images (显示内容便于查看,所以不完整)
gcr.io/google_containers/pause-amd64 3.0
index.tenxcloud.com/google_containers/kube2sky 1.11
index.tenxcloud.com/google_containers/etcd 2.0.9
index.tenxcloud.com/google_containers/skydns 2015-03-11-001
----------------------------------------------------
# kubectl create -f dns/kubedns-rc.yaml --validate//检查文件的正确性并创建
# kubectl create -f dns/kubedns-service.yaml
# kubectl get rc
NAME DESIRED CURRENT AGE
kube-dns-v6 1 1 38m
# kubectl get svc
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kube-dns 10.254.0.10 53/UDP,53/TCP 38m
kubernetes 10.254.0.1 443/TCP 5h
# kubectl get svc -o wide // -o wide 参数显示详细信息
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR
kube-dns 10.254.0.10 53/UDP,53/TCP 2d k8s-app=kube-dns
kubernetes 10.254.0.1 443/TCP 3d
2.测试DNS 是否正常解析：
首先分别创建一个名为：mysql-service的service 和 busybox的pod
# cat mysql-server.yaml
apiVersion: v1
kind: Service
metadata:
labels:
name: mysql
role: service
name: mysql-service
spec:
type: NodePort
ports:
- port: 3306
targetPort: 3306
nodePort: 31000
selector:
name: mysql
# cat busybox.yaml
apiVersion: v1
kind: Pod
metadata:
labels:
name: busybox
role: master
name: busybox
spec:
containers:
- name: busybox
image: busybox
command:
- sleep
- "360000"
# kubectl create -f mysql-server.yaml
# kubectl create -f busybox.yaml
# kubectl get svc
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kube-dns 10.254.0.10 53/UDP,53/TCP 41m
kubernetes 10.254.0.1 443/TCP 5h
mysql-service 10.254.155.188 3306/TCP 41m
# kubectl get pod -o wide
NAME READY STATUS RESTARTS AGE IP NODE
busybox 1/1 Running 0 2d 10.1.77.2 node1
kube-dns-v6-dfucv 3/3 Running 0 2d 10.1.62.2 node2
# kubectl exec -i -t busybox sh
/ # nslookup mysql-service
Server: 10.254.0.10
Address 1: 10.254.0.10
Name: mysql-service
Address 1: 10.254.155.188
/ # nslookup mysql-service.default.kube.local
Server: 10.254.0.10
Address 1: 10.254.0.10
Name: mysql-service.default.kube.local
Address 1: 10.254.155.188
/ #nslookup mysql-service.default.svc.kube.local
Server: 10.254.0.10
Address 1: 10.254.0.10
Name: mysql-service.default.svc.kube.local
Address 1: 10.254.155.188
/// 可以看到mysql-service、mysql-service.default.svc.kube.local、mysql-service.default.kube.local的域名均能正确解析为mysql-service的service中的 10.254.155.188。
/// mysql-service.default.kube.local为完整域名，其组成为..
扩展命令操作
- # kubectl get rc --namespace=kube-system 查询指定命名空间
- # kubectl get pod --all-namespaces=true 查询所有命名空间
3. 最后在简单介绍下kubernetes dns的原理。
首先在部署时候创建了一个dns的rc，最终会产生三个容器(不含pause)
# docker ps -a // 根据上面的 kubectl get pod -o wide运行在node2 节点
CONTAINER> 033800f393b9 index.alauda.cn/tutum/centos:centos6 "/run.sh" 3 days ago Up 3 days 22/tcp awesome_newton
0fb60dcfb8b4 gcr.io/google_containers/etcd:2.0.9 "/usr/local/bin/etcd " 3 days ago Up 3 days k8s_etcd.8d001f7f_kube-dns-v6-ju8cb_default_149fdba5-4e50-11e6-ba47-0800273d5f3f_6afe5c27
0a0efd5f0aaa gcr.io/google_containers/skydns:2015-03-11-001 "/skydns -machines=ht" 3 days ago Up 3 days k8s_skydns.5d0f4a29_kube-dns-v6-ju8cb_default_149fdba5-4e50-11e6-ba47-0800273d5f3f_f7c4ee06
cfef318e4032 gcr.io/google_containers/kube2sky:1.11 "/kube2sky --kube_mas" 3 days ago Up 3 days k8s_kube2sky.eb7ac18c_kube-dns-v6-ju8cb_default_149fdba5-4e50-11e6-ba47-0800273d5f3f_19b79770
afad7b2ebd3d docker.io/kubernetes/pause "/pause" 3 days ago Up 3 days k8s_POD.87e723e6_kube-dns-v6-ju8cb_default_149fdba5-4e50-11e6-ba47-0800273d5f3f_3c3f7c87
【dns解析过程】
在创建的pod中，可以查看其所使用的域名解析服务器:
# kubectl exec -i -t busybox sh
/ # cat /etc/resolv.conf
search default.svc.kube.local svc.kube.local kube.local
nameserver 10.254.0.10
options ndots:5
在kubelet创建pod时，会使用为kubelet配置的-cluster_dns=10.254.0.10 --cluster_domain=kube.local，在创建的pod中从而使用对应的dns服务器。
而这一dns解析服务，实际是由dns的rc中的gcr.io/google_containers/skydns:2015-03-11-001容器0a0efd5f0aaa完成的。
skydns的数据源来自于gcr.io/google_containers/etcd:2.0.9的容器0fb60dcfb8b4。
# docker exec -it 0fb etcdctl get /skydns/local/kube/svc/default/mysql-service/2f1020d6
{"host":"10.254.162.44","priority":10,"weight":10,"ttl":30,"targetstrip":0}
# docker exec -it 0fb etcdctl get /skydns/local/kube/default/mysql-service
{"host":"10.254.162.44","priority":10,"weight":10,"ttl":30,"targetstrip":0}
【service同步过程】
etcd的数据源自于gcr.io/google_containers/kube2sky:1.11创建的cfef318e4032容器。
cfef318e4032容器通过watch kube-api的service，查看service的变化。
当service创建/删除/修改时，cfef318e4032容器获取对应的service信息，将其保存在etcd的容器0fb60dcfb8b4中，进而提供给skydns使用。
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