之前写了很多kubernetes源码阅读的文章，今天介绍一下kubernetes开发入门，kubernetes提供了一个client-go，它里面封装了kubernetes的相关操作，分为两种情况，在集群内核集群之外
先说一下集群内

package main

import (
    "fmt"
    "time"

    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/rest"
)

func main() {
    // creates the in-cluster config
    config, err := rest.InClusterConfig()
    if err != nil {
        panic(err.Error())
    }
    // creates the clientset
    clientset, err := kubernetes.NewForConfig(config)
    if err != nil {
        panic(err.Error())
    }
    for {
        pods, err := clientset.CoreV1().Pods("").List(metav1.ListOptions{})
        if err != nil {
            panic(err.Error())
        }
        fmt.Printf("There are %d pods in the cluster\n", len(pods.Items))
        time.Sleep(10 * time.Second)
    }
}

代码很简单，其实是通过kubernetes自身的服务发现去完成的，kubernetes自带的service；访问token也通过secret的方式注入到容器里面，这样容器里面就可以调用kubernetes的api了。
如果是集群之外去访问的话就只能通过kubeconfig文件了。

package main

import (
    "flag"
    "fmt"
    "time"

    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/apimachinery/pkg/fields"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/tools/cache"
    "k8s.io/client-go/pkg/api/v1"
    "k8s.io/client-go/tools/clientcmd"
    // Uncomment the following line to load the gcp plugin (only required to authenticate against GKE clusters).
    // _ "k8s.io/client-go/plugin/pkg/client/auth/gcp"
)

func main() {
    kubeconfig := flag.String("kubeconfig", "/mnt/go/src/k8s.io/client-go/examples/out-of-cluster/config", "absolute path to the kubeconfig file")
    flag.Parse()
    // uses the current context in kubeconfig
    config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
    if err != nil {
        panic(err.Error())
    }
    // creates the clientset
    clientset, err := kubernetes.NewForConfig(config)
    if err != nil {
        panic(err.Error())
    }

    watchlist := cache.NewListWatchFromClient(clientset.Core().RESTClient(), "pods", v1.NamespaceDefault,
        fields.Everything())
    _, controller := cache.NewInformer(
        watchlist,
        &v1.Pod{},
        time.Second * 0,
        cache.ResourceEventHandlerFuncs{
            AddFunc: func(obj interface{}) {
                fmt.Printf("add: %s \n", obj)
            },
            DeleteFunc: func(obj interface{}) {
                fmt.Printf("delete: %s \n", obj)
            },
            UpdateFunc:func(oldObj, newObj interface{}) {
                fmt.Printf("old: %s, new: %s \n", oldObj, newObj)
            },
        },
    )
    stop := make(chan struct{})
    go controller.Run(stop)


    for {
        pods, err := clientset.CoreV1().Pods("").List(metav1.ListOptions{})
        if err != nil {
            panic(err.Error())
        }
        fmt.Printf("There are %d pods in the cluster\n", len(pods.Items))
        time.Sleep(10 * time.Second)
    }
}

上面代码通过kubeconfig建立连接，通过watchlist的方式监听pods的变化，监听add/delete/update事件。