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本文将在前文的基础上介绍在 kubernetes 集群环境中配置 dns 服务，在 k8s 集群中，pod 的生命周期是短暂的，pod 重启后 ip 地址会产生变化，对于应用程序来说这是不可接受的，为解决这个问题，K8S 集群巧妙的引入的 dns 服务来实现服务的发现，在 k8s 集群中 dns 总共需要使用 4 个组件，各组件分工如下：
etcd：DNS 存储
kube2sky：将 Kubernetes Master 中的 service（服务）注册到 etcd。
skyDNS：提供 DNS 域名解析服务。
healthz：提供对 skydns 服务的健康检查。
一、下载相关镜像文件，并纳入本地仓库统一管理
# docker pull docker.io/elcolio/etcd
# docker pull docker.io/port/kubernetes-kube2sky
# docker pull docker.io/skynetservices/skydns
# docker pull docker.io/wu1boy/healthz
# docker tag docker.io/elcolio/etcd registry.fjhb.cn/etcd
# docker tag docker.io/port/kubernetes-kube2sky registry.fjhb.cn/kubernetes-kube2sky
# docker tag docker.io/skynetservices/skydns registry.fjhb.cn/skydns
# docker tag docker.io/wu1boy/healthz registry.fjhb.cn/healthz
# docker push registry.fjhb.cn/etcd
# docker push registry.fjhb.cn/kubernetes-kube2sky
# docker push registry.fjhb.cn/skydns
# docker push registry.fjhb.cn/healthz
# docker images |grep fjhb
二、通过 rc 文件创建 pod
这里面一个 pod 包含了 4 个组件，一个组件运行在一个 docker 容器中
# cat skydns-rc.yaml
apiVersion: v1
kind: ReplicationController
metadata:
name: kube-dns
namespace: default
labels:
k8s-app: kube-dns
version: v12
kubernetes.io/cluster-service: “true”
spec:
replicas: 1
selector:
k8s-app: kube-dns
version: v12
template:
metadata:
labels:
k8s-app: kube-dns
version: v12
kubernetes.io/cluster-service: “true”
spec:
containers:
– name: etcd
image: registry.fjhb.cn/etcd
resources:
limits:
cpu: 100m
memory: 50Mi
requests:
cpu: 100m
memory: 50Mi
command:
– /bin/etcd
– –data-dir
– /tmp/data
– –listen-client-urls
– http://127.0.0.1:2379,http://127.0.0.1:4001
– –advertise-client-urls
– http://127.0.0.1:2379,http://127.0.0.1:4001
– –initial-cluster-token
– skydns-etcd
volumeMounts:
– name: etcd-storage
mountPath: /tmp/data
– name: kube2sky
image: registry.fjhb.cn/kubernetes-kube2sky
resources:
limits:
cpu: 100m
memory: 50Mi
requests:
cpu: 100m
memory: 50Mi
args:
– -kube_master_url=http://192.168.115.5:8080
– -domain=cluster.local
– name: skydns
image: registry.fjhb.cn/skydns
resources:
limits:
cpu: 100m
memory: 50Mi
requests:
cpu: 100m
memory: 50Mi
args:
– -machines=http://127.0.0.1:4001
– -addr=0.0.0.0:53
– -ns-rotate=false
– -domain=cluster.local
ports:
– containerPort: 53
name: dns
protocol: UDP
– containerPort: 53
name: dns-tcp
protocol: TCP
– name: healthz
image: registry.fjhb.cn/healthz
resources:
limits:
cpu: 10m
memory: 20Mi
requests:
cpu: 10m
memory: 20Mi
args:
– -cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1 >/dev/null
– -port=8080
ports:
– containerPort: 8080
protocol: TCP
volumes:
– name: etcd-storage
emptyDir: {}
dnsPolicy: Default
三、通过 srv 文件创建 service
# cat skydns-svc.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: 10.254.16.254
ports:
– name: dns
port: 53
protocol: UDP
– name: dns-tcp
port: 53
protocol: TCP# kubectl create -f skydns-rc.yaml
# kubectl create -f skydns-svc.yaml
# kubectl get rc
# kubectl get pod
# kubectl get svc
# kubectl describe svc kube-dns
# kubectl describe rc kube-dns
# kubectl describe pod kube-dns-9fllp
Name: kube-dns-9fllp
Namespace: default
Node: 192.168.115.6/192.168.115.6
Start Time: Tue, 23 Jan 2018 10:55:19 -0500
Labels: k8s-app=kube-dns
kubernetes.io/cluster-service=true
version=v12
Status: Running
IP: 172.16.37.5
Controllers: ReplicationController/kube-dns
Containers:
etcd:
Container ID: docker://62ad76bfaca1797c5f43b0e9eebc04074169fce4cc15ef3ffc4cd19ffa9c8c19
Image: registry.fjhb.cn/etcd
Image ID: docker-pullable://docker.io/elcolio/etcd@sha256:3b4dcd35a7eefea9ce2970c81dcdf0d0801a778d117735ee1d883222de8bbd9f
Port:
Command:
/bin/etcd
–data-dir
/tmp/data
–listen-client-urls
http://127.0.0.1:2379,http://127.0.0.1:4001
–advertise-client-urls
http://127.0.0.1:2379,http://127.0.0.1:4001
–initial-cluster-token
skydns-etcd
Limits:
cpu: 100m
memory: 50Mi
Requests:
cpu: 100m
memory: 50Mi
State: Running
Started: Tue, 23 Jan 2018 10:55:23 -0500
Ready: True
Restart Count: 0
Volume Mounts:
/tmp/data from etcd-storage (rw)
/var/run/secrets/kubernetes.io/serviceaccount from default-token-6pddn (ro)
Environment Variables: <none>
kube2sky:
Container ID: docker://6b0bc6e8dce83e3eee5c7e654fbaca693730623fb7936a1fd9d73de1a1dd8152
Image: registry.fjhb.cn/kubernetes-kube2sky
Image ID: docker-pullable://docker.io/port/kubernetes-kube2sky@sha256:0230d3fbb0aeb4ddcf903811441cf2911769dbe317a55187f58ca84c95107ff5
Port:
Args:
-kube_master_url=http://192.168.115.5:8080
-domain=cluster.local
Limits:
cpu: 100m
memory: 50Mi
Requests:
cpu: 100m
memory: 50Mi
State: Running
Started: Tue, 23 Jan 2018 10:55:25 -0500
Ready: True
Restart Count: 0
Volume Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from default-token-6pddn (ro)
Environment Variables: <none>
skydns:
Container ID: docker://ebc2aaaa54e2f922e370e454ec537665d813c69d37a21e3afd908e6dad056627
Image: registry.fjhb.cn/skydns
Image ID: docker-pullable://docker.io/skynetservices/skydns@sha256:6f8a9cff0b946574bb59804016d3aacebc637581bace452db6a7515fa2df79ee
Ports: 53/UDP, 53/TCP
Args:
-machines=http://127.0.0.1:4001
-addr=0.0.0.0:53
-ns-rotate=false
-domain=cluster.local
Limits:
cpu: 100m
memory: 50Mi
Requests:
cpu: 100m
memory: 50Mi
State: Running
Started: Tue, 23 Jan 2018 10:55:27 -0500
Ready: True
Restart Count: 0
Volume Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from default-token-6pddn (ro)
Environment Variables: <none>
healthz:
Container ID: docker://f1de1189fa6b51281d414d7a739b86494b04c8271dc6bb5f20c51fac15ec9601
Image: registry.fjhb.cn/healthz
Image ID: docker-pullable://docker.io/wu1boy/healthz@sha256:d6690c0a8cc4f810a5e691b6a9b8b035192cb967cb10e91c74824bb4c8eea796
Port: 8080/TCP
Args:
-cmd=nslookup kubernetes.default.svc.cluster.local 127.0.0.1 >/dev/null
-port=8080
Limits:
cpu: 10m
memory: 20Mi
Requests:
cpu: 10m
memory: 20Mi
State: Running
Started: Tue, 23 Jan 2018 10:55:29 -0500
Ready: True
Restart Count: 0
Volume Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from default-token-6pddn (ro)
Environment Variables: <none>
Conditions:
Type Status
Initialized True
Ready True
PodScheduled True
Volumes:
etcd-storage:
Type: EmptyDir (a temporary directory that shares a pod’s lifetime)
Medium:
default-token-6pddn:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-6pddn
QoS Class: Guaranteed
Tolerations: <none>
Events:
FirstSeen LastSeen Count From SubObjectPath Type Reason Message
——— ——– —– —- ————- ——– —— ——-
7m 7m 1 {default-scheduler} Normal Scheduled Successfully assigned kube-dns-9fllp to 192.168.115.6
7m 7m 1 {kubelet 192.168.115.6} spec.containers{etcd} Normal Pulling pulling image “registry.fjhb.cn/etcd”
7m 7m 1 {kubelet 192.168.115.6} spec.containers{etcd} Normal Pulled Successfully pulled image “registry.fjhb.cn/etcd”
7m 7m 1 {kubelet 192.168.115.6} spec.containers{etcd} Normal Created Created container with docker id 62ad76bfaca1; Security:[seccomp=unconfined]
7m 7m 1 {kubelet 192.168.115.6} spec.containers{kube2sky} Normal Pulled Successfully pulled image “registry.fjhb.cn/kubernetes-kube2sky”
7m 7m 1 {kubelet 192.168.115.6} spec.containers{etcd} Normal Started Started container with docker id 62ad76bfaca1
7m 7m 1 {kubelet 192.168.115.6} spec.containers{kube2sky} Normal Pulling pulling image “registry.fjhb.cn/kubernetes-kube2sky”
7m 7m 1 {kubelet 192.168.115.6} spec.containers{kube2sky} Normal Created Created container with docker id 6b0bc6e8dce8; Security:[seccomp=unconfined]
7m 7m 1 {kubelet 192.168.115.6} spec.containers{skydns} Normal Pulled Successfully pulled image “registry.fjhb.cn/skydns”
7m 7m 1 {kubelet 192.168.115.6} spec.containers{skydns} Normal Pulling pulling image “registry.fjhb.cn/skydns”
7m 7m 1 {kubelet 192.168.115.6} spec.containers{kube2sky} Normal Started Started container with docker id 6b0bc6e8dce8
7m 7m 1 {kubelet 192.168.115.6} spec.containers{skydns} Normal Created Created container with docker id ebc2aaaa54e2; Security:[seccomp=unconfined]
7m 7m 1 {kubelet 192.168.115.6} spec.containers{skydns} Normal Started Started container with docker id ebc2aaaa54e2
7m 7m 1 {kubelet 192.168.115.6} spec.containers{healthz} Normal Pulling pulling image “registry.fjhb.cn/healthz”
7m 7m 1 {kubelet 192.168.115.6} spec.containers{healthz} Normal Pulled Successfully pulled image “registry.fjhb.cn/healthz”
7m 7m 1 {kubelet 192.168.115.6} spec.containers{healthz} Normal Created Created container with docker id f1de1189fa6b; Security:[seccomp=unconfined]
7m 7m 1 {kubelet 192.168.115.6} spec.containers{healthz} Normal Started Started container with docker id f1de1189fa6b
四、修改 kubelet 配置文件并重启服务
注意:
–cluster-dns 参数要和前面 svc 文件中的 clusterIP 参数一致
–cluster-domain 参数要和前面 rc 文件中的 -domain 参数一致
集群内所有的 kubelet 节点都需要修改
# grep ‘KUBELET_ADDRESS’ /etc/kubernetes/kubelet
KUBELET_ADDRESS=”–address=192.168.115.5 –cluster-dns=10.254.16.254 –cluster-domain=cluster.local”
# systemctl restart kubelet
五、运行一个 busybox 和 curl 进行测试
# cat busybox.yaml
apiVersion: v1
kind: Pod
metadata:
name: busybox
spec:
containers:
– name: busybox
image: docker.io/busybox
command:
– sleep
– “3600”# cat curl.yaml
apiVersion: v1
kind: Pod
metadata:
name: curl
spec:
containers:
– name: curl
image: docker.io/webwurst/curl-utils
command:
– sleep
– “3600”# kubectl create -f busybox.yaml
# kubectl create -f curl.yaml
通过 busybox 容器对 kubernetes 的 service 进行解析，发现 service 被自动解析成了对应的集群 ip 地址，而并不是 172.16 网段的 docker 地址
# kubectl get svc
# kubectl exec busybox — nslookup frontend
# kubectl exec busybox — nslookup Redis-master
# kubectl exec busybox — nslookup redis-slave
通过 curl 容器访问前面创建的 php 留言板
# kubectl exec curl — curl frontend
