Java连接kubernates集群最优雅的两种方式

创建maven工程，pom.xml中引入连接k8s的客户端jar包：

<properties>
  <maven.compiler.source>8maven.compiler.source>
  <maven.compiler.target>8maven.compiler.target>
  <fabric.io.version>6.10.0fabric.io.version>
properties>

<dependencies>
  <dependency>
    <groupId>io.fabric8groupId>
    <artifactId>kubernetes-clientartifactId>
    <version>${fabric.io.version}version>
  dependency>
dependencies>

目标：使用尽可能少的配置项来完成初始化工作，保证后续部署工作量最小

使用kubeconfig文件连接集群

使用场景

可以获取集群的kubeconfig文件

环境变量配置

默认配置项：

KUBECONFIG=~/.kube/config

自定义配置：

KUBECONFIG=/opt/file/kubeconfig

示例代码

import io.fabric8.kubernetes.api.model.Namespace;
import io.fabric8.kubernetes.api.model.NamespaceList;
import io.fabric8.kubernetes.client.KubernetesClient;
import io.fabric8.kubernetes.client.KubernetesClientBuilder;

public class K8sClientWithKubeConfig {
    public static void main(String[] args) {
        KubernetesClient client = new KubernetesClientBuilder().build();
        System.out.println(client.getMasterUrl());
        NamespaceList myNs = client.namespaces().list();

        for (Namespace ns : myNs.getItems()) {
            System.out.println(ns.getMetadata().getName());
        }
        client.close();
    }
}

其中master url为kubeconfig文件中的server字段；

使用ServiceAccount连接集群

使用场景

应用部署在k8s集群内，且可以创建Service Account和进行授权等操作（RBAC）

创建SA

apiVersion: v1
kind: ServiceAccount
metadata:
 name: fmuser

---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
 name: fmuser-role
rules:
 - apiGroups: [""]
   resources: ["pods", "namespaces"]
   verbs: ["get", "list", "watch"]
 - apiGroups: [""]
   resources: ["pods/log"]
   verbs: ["get", "list", "watch"]
 - apiGroups: [""]
   resources: ["pods"]
   verbs: ["delete"]
 - apiGroups: [""]
   resources: ["namespaces"]
   verbs: ["get", "list", "watch"]

---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
 name: fmuser-rolebinding
subjects:
 - kind: ServiceAccount
   name: fmuser
   namespace: default
roleRef:
 kind: ClusterRole
 name: fmuser-role
 apiGroup: rbac.authorization.k8s.io

资源授权根据实际使用情况设置即可，Role（当前空间，权限较小）和ClusterRole（整个集群，权限较大）根据需要创建；在代码中使用时，不需要额外配置，客户端会从以下路径自动读取：

/home/app # ls -l /var/run/secrets/kubernetes.io/serviceaccount/
total 0
lrwxrwxrwx    1 root     root            13 Jan 22 02:55 ca.crt -> ..data/ca.crt
lrwxrwxrwx    1 root     root            16 Jan 22 02:55 namespace -> ..data/namespace
lrwxrwxrwx    1 root     root            12 Jan 22 02:55 token -> ..data/token
/home/app #

所需的文件就是ca.crt和token；
如果需要在集群外验证这种认证方式，需要设置如下环境变量：

KUBERNETES_MASTER=https://191.168.7.132:6443;
KUBERNETES_AUTH_SERVICEACCOUNT_TOKEN=/opt/file/serviceaccount-token;
KUBERNETES_CERTS_CA_FILE=/opt/file/serviceaccount-ca.key;
KUBERNETES_AUTH_TRYKUBECONFIG=false

其中serviceaccount-ca.key和serviceaccount-token对应的是上面的ca.crt和token，需要注意的是，使用这种方式，master的url中的端口是6443，而不是默认的443，需要注意；

示例代码

import io.fabric8.kubernetes.api.model.Namespace;
import io.fabric8.kubernetes.api.model.NamespaceList;
import io.fabric8.kubernetes.client.KubernetesClient;
import io.fabric8.kubernetes.client.KubernetesClientBuilder;

public class K8sClientWithServiceAccount {
    public static void main(String[] args) {
        KubernetesClient client = new KubernetesClientBuilder().build();
        System.out.println(client.getConfiguration().getCaCertFile());
        System.out.println(client.getConfiguration().getMasterUrl());
        System.out.println(client.getConfiguration().getAutoOAuthToken());
        NamespaceList myNs = client.namespaces().list();

        for (Namespace ns : myNs.getItems()) {
            System.out.println(ns.getMetadata().getName());
        }
        client.close();
    }
}

打印的值就是环境变量中设置的；

获取sa的ca.crt和token

root@tianshu-ai-platform:~# kubectl get sa
NAME      SECRETS   AGE
default   1         13d
fmuser    1         7d
test      1         7d
root@tianshu-ai-platform:~# kubectl describe sa fmuser
Name:                fmuser
Namespace:           default
Labels:              
Annotations:         
Image pull secrets:  
Mountable secrets:   fmuser-token-9qb8n
Tokens:              fmuser-token-9qb8n
Events:              
root@tianshu-ai-platform:~# kubectl describe secret fmuser-token-9qb8n
Name:         fmuser-token-9qb8n
Namespace:    default
Labels:       
Annotations:  kubernetes.io/service-account.name: fmuser
              kubernetes.io/service-account.uid: 012db65a-e482-4626-ba01-fc136786c5b1

Type:  kubernetes.io/service-account-token

Data
====
ca.crt:     1066 bytes
namespace:  7 bytes
token:      eyJhbGciOiJSUzI1NiIsImtpZCI6IjJ5SVZq......

root@tianshu-ai-platform:~# kubectl get secret fmuser-token-9qb8n -o jsonpath='{.data.ca\.crt}'
LS0tLS1CRUdJTiBDRVJ....
root@tianshu-ai-platform:~# kubectl get secret fmuser-token-9qb8n -o jsonpath='{.data.token}'
ZXlKaGJHY2lPaUpTVXpJ.....

root@tianshu-ai-platform:~# kubectl get secret fmuser-token-9qb8n -o jsonpath='{.data.ca\.crt}' | base64 --decode
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

root@tianshu-ai-platform:~# kubectl get secret fmuser-token-9qb8n -o jsonpath='{.data.token}' | base64 --decode
eyJhbGciOiJSUzI1NiIsImtpZCI6IjJ5SVZqUjBOLVdwbUluU2F5M....

在使用中的ca.crt和token都是base64解码过的，存储在secret中的都是经过编码的；