三，k8s集群的应用入门
kubernetes集群简单应用
kubectl常用命令：
kubectl cluster-info #查看集群信息
kubectl describe pod -n kube-system kube-flannel-ds-amd64-trpqq #查看pod的描述信息
kubectl get pods -n kube-system #查看指定命名空间的pod
kubectl create deployment NAME --image=image [--dry-run] [options] #创建deployment, dry-run为true就是测试不执行
kubectl create serviceaccount admin -o yaml --dry-run #针对所有可以用kubectl create 创建的资源，都可以加 -o yaml --dry-run ，用来导出yaml标准格式的文件。
kubectl expose deployment nginx-deploy --name=nginx --port=80 --target-port=80 --protocol=TCP
#为deployment创建service, --name为service的名字, --port为暴露端口, --target-port为目标pod端口
dig -t A nginx.default.svc.cluster.local @10.96.0.10 #验证是否能正确解析service, @后边的ip为k8s的dns地址
kubectl describe svc nginx #查看名为nginx的这个service的详细信息
kubectl get pods --show-labels #查看pod的标签
kubectl scale deployment nginx-deploy --replicas=3 #扩容或缩容, --replicas为数量
wget -O - -q nginx-deploy
kubectl rollout undo deployment myapp-deploy --to-revision=1 #回滚到指定版本, 默认回滚到上一版本
kubectl explain pod #查看pod用法的详细信息（参数选项等）
创建pod
使用kubectl run 来增加一个pod，使用nginx的镜像，开放80端口，副本数为 1
[root@master ~]# kubectl run nginx-deploy --image=nginx:1.14-alpine --port=80 --replicas=1
kubectl run --generator=deployment/apps.v1 is DEPRECATED and will be removed in a future version. Use kubectl run --generator=run-pod/v1 or kubectl create instead.
deployment.apps/nginx-deploy created
查看
在第一次查看时，因为nginx镜像还需要时间拖拽下来，看到的是还在创建中
也可以使用 -o wide 来查看详细信息
[root@master ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
nginx-deploy-7689897d8d-9dh5s 0/1 ContainerCreating 0 6s
[root@master ~]# kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-deploy-7689897d8d-9dh5s 0/1 ContainerCreating 0 12s <none> node03.kubernetes <none> <none>
当镜像拖拽完成后，pod就被创建成功了。
[root@master ~]# kubectl get deployment -o wide
NAME READY UP-TO-DATE AVAILABLE AGE CONTAINERS IMAGES SELECTOR
nginx-deploy 1/1 1 1 31s nginx-deploy nginx:1.14-alpine run=nginx-deploy
[root@master ~]# kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-deploy-7689897d8d-9dh5s 1/1 Running 0 50s 10.244.1.2 node03.kubernetes <none> <none>
能看到详细信息中，该pod所对应的容器呗创建在node03 上，并且ip地址是：10.244.1.2，目前只能在Kubernetes节点上才能访问，跳过之外是不能访问的。
[root@master ~]# curl 10.244.1.2
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
body {
width: 35em;
margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif;
}
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>
<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>
<p><em>Thank you for using nginx.</em></p>
</body>
</html>
service创建
事实上，上述的访问是不可取的，虽然可以访问，但容器的ip可能随时都会被修改或者其他情况导致该ip不可被访问。
此时就需要使用到 service 固定访问端点。使用 kubectl expose 来创建。
使用说明如下:
Usage:
kubectl expose (-f FILENAME | TYPE NAME) [--port=port] [--protocol=TCP|UDP|SCTP] [--target-port=number-or-name]
[--name=name] [--external-ip=external-ip-of-service] [--type=type] [options]
注意： --target-port 表示容器上的端口，--name 表示service的名称，而 --port 表示service暴露的端口
--type=type 类型有： ClusterIP, NodePort, LoadBalancer, or ExternalName. Default is 'ClusterIP'.
下面开始创建：
[root@master ~]# kubectl expose deployment nginx-deploy --name=nginx --port=80 --target-port=80 --protocol=TCP
service/nginx exposed
查看
[root@master ~]# kubectl get service
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 17h
nginx ClusterIP 10.105.233.197 <none> 80/TCP 6s
测试访问:
这里的访问，直接访问刚刚创建的nginx service所对应的ip
[root@master ~]# curl 10.105.233.197
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
body {
width: 35em;
margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif;
}
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>
<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>
<p><em>Thank you for using nginx.</em></p>
</body>
</html>
这里需要用到coreDNS，来解析对应的service，这样外部即可访问。要配置coreDNS的域名解析才可。
测试其他pod通过series访问nginx
在master上查看kube-dns 信息
[root@master ~]# kubectl get service -n kube-system
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kube-dns ClusterIP 10.96.0.10 <none> 53/UDP,53/TCP,9153/TCP 17h
创建一个pod，并使用 -it 参数进入到容器中。
[root@master ~]# kubectl run -i -t busybox --image=busybox --restart=Never
If you don't see a command prompt, try pressing enter.
/ #
查看 resolv.conf 文件中DNS
/ # cat /etc/resolv.conf
nameserver 10.96.0.10
search default.svc.cluster.local svc.cluster.local cluster.local localdomain
options ndots:5
尝试解析nginx service
/ # nslookup nginx
Server: 10.96.0.10
Address: 10.96.0.10:53
Name: nginx.default.svc.cluster.local
Address: 10.105.233.197
/ # nslookup nginx.default.svc.cluster.local
Server: 10.96.0.10
Address: 10.96.0.10:53
*** Can't find nginx.default.svc.cluster.local: No answer
可以看到可以解析，尝试访问：
/ # wget -O - -q http://nginx
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
body {
width: 35em;
margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif;
}
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>
<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>
<p><em>Thank you for using nginx.</em></p>
</body>
</html>
可以直接在busybox中访问 刚刚创建的nginx，没问题。
测试手动变更nginx对应的pod的ip
手动删除一下nginx的pod，这样，ip就会变更，然后在busybox中使用相同的service端点看能否访问。
[root@master ~]# kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
busybox 1/1 Running 0 13m 10.244.2.2 node02.kubernetes <none> <none>
nginx-deploy-7689897d8d-9dh5s 1/1 Running 0 60m 10.244.1.2 node03.kubernetes <none> <none>
[root@master ~]# kubectl delete pod nginx-deploy-7689897d8d-9dh5s
pod "nginx-deploy-7689897d8d-9dh5s" deleted
[root@master ~]# kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
busybox 1/1 Running 0 13m 10.244.2.2 node02.kubernetes <none> <none>
nginx-deploy-7689897d8d-lf8p7 1/1 Running 0 13s 10.244.3.2 node01.kubernetes <none> <none>
可以看到，nginx-deploy 的ip已经变更，下面测试访问
/ # wget -O - -q http://nginx
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
body {
width: 35em;
margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif;
}
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>
<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>
<p><em>Thank you for using nginx.</em></p>
</body>
</html>
依然可以访问。
pod和service之间的关系
查看 nginx 的service 对应的详细信息；
[root@master ~]# kubectl describe svc nginx
Name: nginx
Namespace: default
Labels: run=nginx-deploy
Annotations: <none>
Selector: run=nginx-deploy
Type: ClusterIP
IP: 10.105.233.197
Port: <unset> 80/TCP
TargetPort: 80/TCP
Endpoints: 10.244.3.2:80
Session Affinity: None
Events: <none>
查看pod标签
[root@master ~]# kubectl get pods --show-labels
NAME READY STATUS RESTARTS AGE LABELS
busybox 1/1 Running 0 30m run=busybox
nginx-deploy-7689897d8d-lf8p7 1/1 Running 0 16m pod-template-hash=7689897d8d,run=nginx-deploy
这里可以看出，因为nginx-deply的pod中，有nginx-deploy标签，而nginx的service的Selector选择的正式nginx-deploy标签，所以会被选中。
这就是pod和service之间的关系
service调度测试
创建一个两个副本的pod
[root@master ~]# kubectl run myapp --image=ikubernetes/myapp:v1 --replicas=2
kubectl run --generator=deployment/apps.v1 is DEPRECATED and will be removed in a future version. Use kubectl run --generator=run-pod/v1 or kubectl create instead.
deployment.apps/myapp created
[root@master ~]# kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
myapp-84cd4b7f95-kzf68 1/1 Running 0 77s 10.244.1.3 node03.kubernetes <none> <none>
myapp-84cd4b7f95-mx5vq 1/1 Running 0 77s 10.244.2.3 node02.kubernetes <none> <none>
在busybox中直接访问myapp
/ # wget -O - -q http://10.244.1.3
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
/ # wget -O - -q http://10.244.1.3/hostname.html
myapp-84cd4b7f95-kzf68
/ # wget -O - -q http://10.244.2.3
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
/ # wget -O - -q http://10.244.2.3/hostname.html
myapp-84cd4b7f95-mx5vq
创建myapp对应的service
[root@master ~]# kubectl expose deployment myapp --name=myapp --port=80
service/myapp exposed
[root@master ~]# kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 18h
myapp ClusterIP 10.108.135.202 <none> 80/TCP 4s
nginx ClusterIP 10.96.12.15 <none> 80/TCP 7m41s
在busybox中访问service
/ # wget -O - -q http://myapp
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
/ # wget -O - -q http://myapp/hostname.html
/ # wget -O - -q http://myapp/hostname.html
myapp-84cd4b7f95-mx5vq
/ # wget -O - -q http://myapp/hostname.html
myapp-84cd4b7f95-kzf68
可以看到，当直接访问对应的service的时候，会有一个轮训的效果，这样就起到了负载均衡效果。
动态扩容pod
刚刚创建的myapp是2个副本，这个副本数是可以动态扩容的.
可以使用 kubectl scale 来扩容
Usage:
kubectl scale [--resource-version=version] [--current-replicas=count] --replicas=COUNT (-f FILENAME | TYPE NAME)
[options]
操作：
[root@master ~]# kubectl scale --replicas=5 deployment myapp
deployment.extensions/myapp scaled
[root@master ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
busybox 1/1 Running 0 46m
myapp-84cd4b7f95-kzf68 1/1 Running 0 9m56s
myapp-84cd4b7f95-mx5vq 1/1 Running 0 9m56s
myapp-84cd4b7f95-nk8l2 1/1 Running 0 25s
myapp-84cd4b7f95-srlt2 1/1 Running 0 25s
myapp-84cd4b7f95-tgsdd 1/1 Running 0 25s
nginx-deploy-7689897d8d-lf8p7 1/1 Running 0 32m
可以看到已经被调动成功，添加到5个副本数。
同时在看service
/ # while true; do wget -O - -q http://myapp/hostname.html;sleep 1;done
myapp-84cd4b7f95-kzf68
myapp-84cd4b7f95-mx5vq
myapp-84cd4b7f95-tgsdd
myapp-84cd4b7f95-mx5vq
myapp-84cd4b7f95-kzf68
myapp-84cd4b7f95-srlt2
myapp-84cd4b7f95-srlt2
myapp-84cd4b7f95-srlt2
myapp-84cd4b7f95-nk8l2
myapp-84cd4b7f95-mx5vq
myapp-84cd4b7f95-mx5vq
myapp-84cd4b7f95-tgsdd
myapp-84cd4b7f95-nk8l2
myapp-84cd4b7f95-srlt2
myapp-84cd4b7f95-mx5vq
myapp-84cd4b7f95-tgsdd
myapp-84cd4b7f95-kzf68
在service中，已经可以被调度了，并且也是负载均衡效果。
这种添加或者减少，直接操作即可。
滚动升级
可以在线的实现灰度、蓝绿等滚动发布升级。
刚刚创建的myapp是v1版本，下面升级到v2版本，然后查看效果。
使用 kubectl set image 来操作
Usage:
kubectl set image (-f FILENAME | TYPE NAME) CONTAINER_NAME_1=CONTAINER_IMAGE_1 ... CONTAINER_NAME_N=CONTAINER_IMAGE_N
[options]
操作：
[root@master ~]# kubectl set image deployment myapp myapp=ikubernetes/myapp:v2
deployment.extensions/myapp image updated
[root@master ~]# kubectl rollout status deployment myapp
Waiting for deployment "myapp" rollout to finish: 2 out of 3 new replicas have been updated...
Waiting for deployment "myapp" rollout to finish: 2 out of 3 new replicas have been updated...
Waiting for deployment "myapp" rollout to finish: 2 out of 3 new replicas have been updated...
Waiting for deployment "myapp" rollout to finish: 1 old replicas are pending termination...
Waiting for deployment "myapp" rollout to finish: 1 old replicas are pending termination...
deployment "myapp" successfully rolled out
可以使用 kubectl rollout status 来跟踪容器的变化
/ # while true; do wget -O - -q http://myapp;sleep 1;done
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
这里也可以看到访问所带来的变化。
同时，因为版本个更新，所有myapp所有的对应的名称的hash值都变化了，因为都被删除后重新创建的。
[root@master ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
busybox 1/1 Running 0 54m
myapp-746644f8d6-96q2j 1/1 Running 0 2m3s
myapp-746644f8d6-qmqdz 1/1 Running 0 114s
myapp-746644f8d6-xj72g 1/1 Running 0 107s
nginx-deploy-7689897d8d-lf8p7 1/1 Running 0 40m
失败回滚
使用 kubectl rollout 来操作
Usage:
kubectl rollout SUBCOMMAND [options]
操作：
[root@master ~]# kubectl rollout undo deployment myapp
deployment.extensions/myapp rolled back
[root@master ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
busybox 1/1 Running 0 57m
myapp-84cd4b7f95-44qch 1/1 Running 0 54s
myapp-84cd4b7f95-fzvsd 1/1 Running 0 55s
myapp-84cd4b7f95-mlphg 1/1 Running 0 52s
nginx-deploy-7689897d8d-lf8p7 1/1 Running 0 44m
查看访问：
while true; do wget -O - -q http://myapp;sleep 1;done
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
开通集群外访问
上面的所有操作，都仅限于kubernetes集群内部的节点所有资源可以访问。
需要修改service中的类型为NodePort，即可开通集群外访问。
[root@master ~]# kubectl edit svc myapp
# Please edit the object below. Lines beginning with a '#' will be ignored,
# and an empty file will abort the edit. If an error occurs while saving this file will be
# reopened with the relevant failures.
#
apiVersion: v1
kind: Service
metadata:
creationTimestamp: "2019-07-10T02:56:26Z"
labels:
run: myapp
name: myapp
namespace: default
resourceVersion: "105517"
selfLink: /api/v1/namespaces/default/services/myapp
uid: 15e48fde-3242-4871-8113-0ae5b91cd634
spec:
clusterIP: 10.108.135.202
externalTrafficPolicy: Cluster
ports:
- nodePort: 31441
port: 80
protocol: TCP
targetPort: 80
selector:
run: myapp
sessionAffinity: None
type: NodePort # 这里修改
status:
loadBalancer: {}
把 type: ClusterIP 修改为 type: NodePort 。
然后保存退出，再次查看myapp的service：
[root@master ~]# kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 18h
myapp NodePort 10.108.135.202 <none> 80:31441/TCP 21m
nginx ClusterIP 10.96.12.15 <none> 80/TCP 29m
能看到myapp的port列中， 80: 31441 ，此时kubernetes中所有节点的31441端口都可以被访问到myapp中的nginx容器
找一台kubernetes集群外的机器访问测试：
[root@guanwang ~]# ip a | grep 255
inet 10.0.20.140/24 brd 10.0.20.255 scope global bond0
[root@guanwang ~]# curl 10.0.20.20:31441
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[root@guanwang ~]# curl 10.0.20.21:31441
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[root@guanwang ~]# curl 10.0.20.22:31441
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[root@guanwang ~]# curl 10.0.20.23:31441
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
以上操作仅仅为了熟悉k8s集群使用的原理，实际应用时大多采用定义yaml资源配置清单方式，下一篇文章将介绍yaml清单配置文件的使用。
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