client-go示例

访问kubernetes集群有几下几种方式：
方式
特点
支持者
Kubernetes dashboard
直接通过Web UI进行操作，简单直接，可定制化程度低
官方支持
kubectl
命令行操作，功能最全，但是比较复杂，适合对其进行进一步的分装，定制功能，版本适配最好
官方支持
​client-go​
从kubernetes的代码中抽离出来的客户端包，简单易用，但需要小心区分kubernetes的API版本
官方支持
​client-python​
python客户端，kubernetes-incubator
官方支持
​Java client​
fabric8中的一部分，kubernetes的java客户端
redhat
下面，我们基于client-go，对Deployment升级镜像的步骤进行了定制，通过命令行传递一个Deployment的名字、应用容器名和新image名字的方式来升级。
kubernetes-client-go-sample
代码如下：
package main
​
import (
    "flag"
    "fmt"
    "os"
    "path/filepath"
​
    "k8s.io/apimachinery/pkg/api/errors"
    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/tools/clientcmd"
)
​
func main() {
    var kubeconfig *string
    if home := homeDir(); home != "" {
        kubeconfig = flag.String("kubeconfig", filepath.Join(home, ".kube", "config"), "(optional) absolute path to the kubeconfig file")
    } else {
        kubeconfig = flag.String("kubeconfig", "", "absolute path to the kubeconfig file")
    }
    deploymentName := flag.String("deployment", "", "deployment name")
    imageName := flag.String("image", "", "new image name")
    appName := flag.String("app", "app", "application name")
​
    flag.Parse()
    if *deploymentName == "" {
        fmt.Println("You must specify the deployment name.")
        os.Exit(0)
    }
    if *imageName == "" {
        fmt.Println("You must specify the new image name.")
        os.Exit(0)
    }
    // use the current context in kubeconfig
    config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
    if err != nil {
        panic(err.Error())
    }
​
    // create the clientset
    clientset, err := kubernetes.NewForConfig(config)
    if err != nil {
        panic(err.Error())
    }
    deployment, err := clientset.AppsV1beta1().Deployments("default").Get(*deploymentName, metav1.GetOptions{})
    if err != nil {
        panic(err.Error())
    }
    if errors.IsNotFound(err) {
        fmt.Printf("Deployment not found\n")
    } else if statusError, isStatus := err.(*errors.StatusError); isStatus {
        fmt.Printf("Error getting deployment%v\n", statusError.ErrStatus.Message)
    } else if err != nil {
        panic(err.Error())
    } else {
        fmt.Printf("Found deployment\n")
        name := deployment.GetName()
        fmt.Println("name ->", name)
        containers := &deployment.Spec.Template.Spec.Containers
        found := false
        for i := range *containers {
            c := *containers
            if c[i].Name == *appName {
                found = true
                fmt.Println("Old image ->", c[i].Image)
                fmt.Println("New image ->", *imageName)
                c[i].Image = *imageName
            }
        }
        if found == false {
            fmt.Println("The application container not exist in the deployment pods.")
            os.Exit(0)
        }
        _, err := clientset.AppsV1beta1().Deployments("default").Update(deployment)
        if err != nil {
            panic(err.Error())
        }
    }
}
​
func homeDir() string {
    if h := os.Getenv("HOME"); h != "" {
        return h
    }
    return os.Getenv("USERPROFILE") // windows
}
我们使用kubeconfig文件认证连接kubernetes集群，该文件默认的位置是$HOME/.kube/config。
该代码编译后可以直接在kubernetes集群之外，任何一个可以连接到API server的机器上运行。
编译运行
$ go get github.com/rootsongjc/kubernetes-client-go-sample
$ cd $GOPATH/src/github.com/rootsongjc/kubernetes-client-go-sample
$ make
$ ./update-deployment-image -h
Usage of ./update-deployment-image:
  -alsologtostderr
        log to standard error as well as files
  -app string
        application name (default "app")
  -deployment string
        deployment name
  -image string
        new image name
  -kubeconfig string
        (optional) absolute path to the kubeconfig file (default "/Users/jimmy/.kube/config")
  -log_backtrace_at value
        when logging hits line file:N, emit a stack trace
  -log_dir string
        If non-empty, write log files in this directory
  -logtostderr
        log to standard error instead of files
  -stderrthreshold value
        logs at or above this threshold go to stderr
  -v value
        log level for V logs
  -vmodule value
        comma-separated list of pattern=N settings for file-filtered logging
使用不存在的image更新
 $ ./update-deployment-image -deployment filebeat-test -image harbor-001.jimmysong.io/library/analytics-docker-test:Build_9 
Found deployment
name -> filebeat-test
Old image -> harbor-001.jimmysong.io/library/analytics-docker-test:Build_8
New image -> harbor-001.jimmysong.io/library/analytics-docker-test:Build_9
查看Deployment的event。
$ kubectl describe deployment filebeat-test   
Name:            filebeat-test
Namespace:        default
CreationTimestamp:    Fri, 19 May 2017 15:12:28 +0800
Labels:            k8s-app=filebeat-test
Selector:        k8s-app=filebeat-test
Replicas:        2 updated | 3 total | 2 available | 2 unavailable
StrategyType:        RollingUpdate
MinReadySeconds:    0
RollingUpdateStrategy:    1 max unavailable, 1 max surge
Conditions:
  Type        Status    Reason
  ----        ------    ------
  Available     True    MinimumReplicasAvailable
  Progressing     True    ReplicaSetUpdated
OldReplicaSets:    filebeat-test-2365467882 (2/2 replicas created)
NewReplicaSet:    filebeat-test-2470325483 (2/2 replicas created)
Events:
  FirstSeen    LastSeen    Count    From                SubObjectPath    Type        ReasoMessage
  ---------    --------    -----    ----                -------------    --------    ------------
  2h        1m        3    {deployment-controller }            Normal        ScalingReplicaSet    Scaled down replica set filebeat-test-2365467882 to 2
  1m        1m        1    {deployment-controller }            Normal        ScalingReplicaSet    Scaled up replica set filebeat-test-2470325483 to 1
  1m        1m        1    {deployment-controller }            Normal        ScalingReplicaSet    Scaled up replica set filebeat-test-2470325483 to 2
可以看到老的ReplicaSet从3个replica减少到了2个，有2个使用新配置的replica不可用，目前可用的replica是2个。
这是因为我们指定的镜像不存在，查看Deployment的pod的状态。
$ kubectl get pods -l k8s-app=filebeat-test
NAME                             READY     STATUS             RESTARTS   AGE
filebeat-test-2365467882-4zwx8   2/2       Running            0          33d
filebeat-test-2365467882-rqskl   2/2       Running            0          33d
filebeat-test-2470325483-6vjbw   1/2       ImagePullBackOff   0          4m
filebeat-test-2470325483-gc14k   1/2       ImagePullBackOff   0          4m
我们可以看到有两个pod正在拉取image。
还原为原先的镜像
将image设置为原来的镜像。
$ ./update-deployment-image -deployment filebeat-test -image harbor-001.jimmysong.io/library/analytics-docker-test:Build_8
Found deployment
name -> filebeat-test
Old image -> harbor-001.jimmysong.io/library/analytics-docker-test:Build_9
New image -> harbor-001.jimmysong.io/library/analytics-docker-test:Build_8
现在再查看Deployment的状态。
$ kubectl describe deployment filebeat-test   
Name:            filebeat-test
Namespace:        default
CreationTimestamp:    Fri, 19 May 2017 15:12:28 +0800
Labels:            k8s-app=filebeat-test
Selector:        k8s-app=filebeat-test
Replicas:        3 updated | 3 total | 3 available | 0 unavailable
StrategyType:        RollingUpdate
MinReadySeconds:    0
RollingUpdateStrategy:    1 max unavailable, 1 max surge
Conditions:
  Type        Status    Reason
  ----        ------    ------
  Available     True    MinimumReplicasAvailable
  Progressing     True    NewReplicaSetAvailable
OldReplicaSets:    <none>
NewReplicaSet:    filebeat-test-2365467882 (3/3 replicas created)
Events:
  FirstSeen    LastSeen    Count    From                SubObjectPath    Type        ReasoMessage
  ---------    --------    -----    ----                -------------    --------    ------------
  2h        8m        3    {deployment-controller }            Normal        ScalingReplicaSet    Scaled down replica set filebeat-test-2365467882 to 2
  8m        8m        1    {deployment-controller }            Normal        ScalingReplicaSet    Scaled up replica set filebeat-test-2470325483 to 1
  8m        8m        1    {deployment-controller }            Normal        ScalingReplicaSet    Scaled up replica set filebeat-test-2470325483 to 2
  2h        1m        3    {deployment-controller }            Normal        ScalingReplicaSet    Scaled up replica set filebeat-test-2365467882 to 3
  1m        1m        1    {deployment-controller }            Normal        ScalingReplicaSet    Scaled down replica set filebeat-test-2470325483 to 0
可以看到available的replica个数恢复成3了。
其实在使用该命令的过程中，通过kubernetes dashboard的页面上查看Deployment的状态更直观，更加方便故障排查。
使用kubernetes dashboard进行故障排查
这也是dashboard最大的优势，简单、直接、高效。

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