部署kubernetes skyDNS
kubernetes可以爲pod提供dns內部域名解析服務。
其主要作用是爲pod提供可以直接通過service的名字解析爲對應service的ip的功能！
1.首先在各節點的kubelet 進程中添加選項：
KUBELET_ARGS="--cluster_dns=10.254.0.10 --cluster_domain=kube.local"
【Master 節點操作如下:】
[root@ master /root/yaml]# 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
[root@ master yaml]# 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負責管理pod的網絡等相關事務: gcr.io/google_containers/pause-amd64:3.0)
谷歌被牆了，可以通過以下方式來使用：
1.***或訪問國內的docker鏡像站點,下載下來改名
[root@ master yaml]# docker pull mritd/pause-amd64:3.0
[root@ master yaml]# docker tag mritd/pause-amd64:3.0 gcr.io/google_containers/pause-amd64:3.0
2.使用內部私有倉庫,在各k8s節點的kubelet 服務進程添加下面參數：
"--pod-infra-container-image=my.hub.io/pause-amd64:3.0"
>>> node 節點鏡像列表 [實際環境中建議使用私有倉庫的鏡像]：
# docker images (顯示內容便於查看,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
----------------------------------------------------
[root@ master yaml]# kubectl create -f dns/kubedns-rc.yaml --validate //檢查文件的正確性並創建
[root@ master yaml]# kubectl create -f dns/kubedns-service.yaml
[root@ master yaml]# kubectl get rc
NAME DESIRED CURRENT AGE
kube-dns-v6 1 1 38m
[root@ master yaml]# kubectl get svc
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kube-dns 10.254.0.10 <none> 53/UDP,53/TCP 38m
kubernetes 10.254.0.1 <none> 443/TCP 5h
[root@ master yaml]# kubectl get svc -o wide // -o wide 參數顯示詳細信息
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR
kube-dns 10.254.0.10 <none> 53/UDP,53/TCP 2d k8s-app=kube-dns
kubernetes 10.254.0.1 <none> 443/TCP 3d <none>
2.測試DNS 是否正常解析：
首先分別創建一個名爲：mysql-service的service 和 busybox的pod
[root@ master yaml]# 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
[root@ master yaml]# cat busybox.yaml
apiVersion: v1
kind: Pod
metadata:
labels:
name: busybox
role: master
name: busybox
spec:
containers:
- name: busybox
image: busybox
command:
- sleep
- "360000"
[root@ master yaml]# kubectl create -f mysql-server.yaml
[root@ master yaml]# kubectl create -f busybox.yaml
[root@ master yaml]# kubectl get svc
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kube-dns 10.254.0.10 <none> 53/UDP,53/TCP 41m
kubernetes 10.254.0.1 <none> 443/TCP 5h
mysql-service 10.254.155.188 <nodes> 3306/TCP 41m
[root@ master yaml]# 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
[root@ master yaml]# 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的域名均能正確解析爲mysql-service的service中的 10.254.155.188。
/// mysql-service.default.kube.local爲完整域名，其組成爲<service-name>.<namespace>.<domain-name>
擴展命令操作<更多命令操作請kubectl --help 或訪問 官方kubectl命令手冊>
- # kubectl get rc --namespace=kube-system 查詢指定命名空間
- # kubectl get pod --all-namespaces=true 查詢所有命名空間
3. 最後在簡單介紹下kubernetes dns的原理。
首先在部署時候創建了一個dns的rc，最終會產生三個容器(不含pause)
[root@ node2 ]# docker ps -a // 根據上面的 kubectl get pod -o wide 運行在node2 節點
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
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解析過程】
在創建的pod中，可以查看其所使用的域名解析服務器:
[root@master ]# 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創建pod時，會使用爲kubelet配置的-cluster_dns=10.254.0.10 --cluster_domain=kube.local，在創建的pod中從而使用對應的dns服務器。
而這一dns解析服務，實際是由dns的rc中的gcr.io/google_containers/skydns:2015-03-11-001容器0a0efd5f0aaa完成的。
skydns的數據源來自於gcr.io/google_containers/etcd:2.0.9的容器0fb60dcfb8b4。
[root@ node2 ]# 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}
[root@ node2]# 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同步過程】
etcd的數據源自於gcr.io/google_containers/kube2sky:1.11創建的cfef318e4032容器。
cfef318e4032容器通過watch kube-api的service，查看service的變化。
當service創建/刪除/修改時，cfef318e4032容器獲取對應的service信息，將其保存在etcd的容器0fb60dcfb8b4中，進而提供給skydns使用。