Kubernetes Java Client Initialization and DSL Usage Guide

Initialize Kubernetes Client

Before using Kubernetes, you need to initialize a client. The default client reads the ~/.kube/config file or the path defined by the KUBECONFIG environment variable. You can also provide a custom Config object to the builder.

try (final KubernetesClient client = new KubernetesClientBuilder().build()) {
    // use client for operations
}

Custom configuration example:

Config kubeConfig = new ConfigBuilder()
    .withMasterUrl("https://192.168.42.20:8443/")
    .build();
try (final KubernetesClient client = new KubernetesClientBuilder().withConfig(kubeConfig).build()) {
    // use client for operations
}

Kubernetes Client DSL Usage

The DSL provides fluent access to all supported resources. Below are representative snippets for Pods, Services, Deployments, and ReplicaSets.

Pods

Access pods via client.pods() . Common operations include loading from YAML, listing, creating, editing, retrieving logs, watching, port‑forwarding, and cleanup.

Pod myPod = client.pods().load(new FileInputStream("some-pod.yml")).item();
PodList podList = client.pods().inNamespace("FunTester").list();
PodList podList = client.pods().inAnyNamespace().list();
PodList podList = client.pods().inNamespace("FunTester").withLabel("foo", "bar").list();
Pod myPod = client.pods().inNamespace("FunTester").withName("nginx-pod").get();
Pod aPod = new PodBuilder().withNewMetadata().withName("demo-pod1").endMetadata()
    .withNewSpec()
    .addNewContainer().withName("nginx").withImage("nginx:1.7.9")
    .addNewPort().withContainerPort(80).endPort()
    .endContainer()
    .endSpec()
    .build();
client.pods().inNamespace("FunTester").resource(aPod).create();
client.pods().inNamespace("FunTester").resource(pod).serverSideApply();
client.pods().inNamespace("FunTester").withName("nginx").edit(p -> new PodBuilder(p).editOrNewMetadata().addToLabels("new", "label").endMetadata().build());
String log = client.pods().inNamespace("FunTester").withName("test-pod").getLog();
LogWatch watch = client.pods().inNamespace(namespace).withName(podName).tailingLines(10).watchLog(System.out);
client.pods().inNamespace("FunTester").withName("nginx").delete();
client.resourceList(pod1, pod2).inNamespace("FunTester").delete();
client.pods().inNamespace("FunTester").withName("nginx").waitUntilReady(5, TimeUnit.MINUTES);
client.pods().inNamespace("FunTester").withName("nginx").waitUntilCondition(pod -> pod.getStatus().getPhase().equals("Succeeded"), 1, TimeUnit.MINUTES);
int containerPort = client.pods().inNamespace("FunTester").withName("testpod").get().getSpec().getContainers().get(0).getPorts().get(0).getContainerPort();
LocalPortForward portForward = client.pods().inNamespace("FunTester").withName("testpod").portForward(containerPort, 8080);

Service

Access services via client.services() . Typical operations include loading from YAML, retrieving, creating, applying, listing, deleting, and watching.

Service aService = client.services().load(new FileInputStream("service.yml")).item();
Service service = client.services().inNamespace("FunTester").withName("some-service").get();
Service createdSvc = client.services().inNamespace("FunTester").resource(svc).create();
client.services().inNamespace("FunTester").resource(svc).serverSideApply();
ServiceList svcList = client.services().inNamespace("FunTester").list();
ServiceList svcList = client.services().inAnyNamespace().list();
ServiceList svcList = client.services().inNamespace("FunTester").withLabel("foo", "bar").list();
client.services().inNamespace("FunTester").withName("some-svc").delete();
client.services().inNamespace("FunTester").watch(new Watcher<>() {
    @Override public void eventReceived(Action action, Service resource) { /* handle */ }
    @Override public void onClose(WatcherException cause) { }
});

Deployment

Access deployments via client.apps().deployments() . Operations cover loading, retrieving, creating, applying, scaling, editing, updating images, rolling restart, pause/resume, undo, delete, and watch.

Deployment aDeployment = client.apps().deployments().load(new FileInputStream("test-deployments.yml")).item();
Deployment deploy = client.apps().deployments().inNamespace("FunTester").withName("deploy-1").get();
Deployment deployment1 = new DeploymentBuilder()
    .withNewMetadata().withName("FunTesterdeployment1").addToLabels("test", "deployment").endMetadata()
    .withNewSpec().withReplicas(1)
    .withNewTemplate().withNewMetadata().addToLabels("app", "httpd").endMetadata()
    .withNewSpec().addNewContainer().withName("busybox").withImage("busybox").withCommand("sleep", "36000").endContainer().endSpec().endTemplate()
    .withNewSelector().addToMatchLabels("app", "httpd").endSelector().endSpec().build();
client.apps().deployments().inNamespace("FunTester").resource(deployment1).create();
client.apps().deployments().inNamespace("FunTester").resource(deployObj).serverSideApply();
DeploymentList aDeploymentList = client.apps().deployments().inNamespace("FunTester").list();
DeploymentList aDeploymentList = client.apps().deployments().inAnyNamespace().list();
DeploymentList aDeployList = client.apps().deployments().inNamespace("FunTester").withLabel("foo", "bar").list();
Deployment updatedDeploy = client.apps().deployments().inNamespace("FunTester").withName("deployment1").edit(d -> new DeploymentBuilder(d).editSpec().withReplicas(2).endSpec().build());
client.apps().deployments().inNamespace("FunTester").withName("ngix-controller").updateImage("docker.io/nginx:latest");
Map
containerToImageMap = new HashMap<>();
containerToImageMap.put("nginx", "nginx:perl");
containerToImageMap.put("sidecar", "someImage:someVersion");
client.apps().deployments().inNamespace("FunTester").withName("nginx-deployment").updateImage(containerToImageMap);
client.apps().deployments().inNamespace("FunTester").withName("nginx-deployment").rolling().restart();
client.apps().deployments().inNamespace("FunTester").withName("nginx-deployment").rolling().pause();
client.apps().deployments().inNamespace("FunTester").withName("nginx-deployment").rolling().resume();
client.apps().deployments().inNamespace("FunTester").withName("nginx-deployment").rolling().undo();
client.apps().deployments().inNamespace("FunTester").withName("foo").delete();
client.apps().deployments().inNamespace("FunTester").watch(new Watcher<>() {
    @Override public void eventReceived(Action action, Deployment resource) { /* handle */ }
    @Override public void onClose(WatcherException cause) { }
});
client.apps().deployments().inNamespace("FunTester").withName("nginx-deployment").scale(1);
client.apps().deployments().inNamespace("FunTester").withName("nginx").watchLog(System.out);

ReplicaSet

Access replica sets via client.apps().replicaSets() . The guide shows loading, retrieving, creating, applying, listing, scaling, updating images, deleting, and watching.

ReplicaSet replicaSet = client.apps().replicaSets().inNamespace("FunTester").load(new FileInputStream("test-replicaset.yml")).item();
ReplicaSet rs = client.apps().replicaSets().inNamespace("FunTester").withName("rs1").get();
ReplicaSet replicaset1 = new ReplicaSetBuilder()
    .withNewMetadata().withName("replicaset1").addToLabels("app", "guestbook").addToLabels("tier", "frontend").endMetadata()
    .withNewSpec().withReplicas(1)
    .withNewSelector().withMatchLabels(Collections.singletonMap("tier", "frontend")).endSelector()
    .withNewTemplate().withNewMetadata().addToLabels("app", "guestbook").addToLabels("tier", "frontend").endMetadata()
    .withNewSpec().addNewContainer().withName("busybox").withImage("busybox").withCommand("sleep", "36000").endContainer().endSpec().endTemplate()
    .endSpec().build();
client.apps().replicaSets().inNamespace("FunTester").resources(replicaset1).create();
client.apps().replicaSets().inNamespace("FunTester").resource(replicaSet).serverSideApply();
ReplicaSetList rsList = client.apps().replicaSets().inNamespace("FunTester").list();
ReplicaSetList rsList = client.apps().replicaSets().inAnyNamespace().list();
ReplicaSetList rsList = client.apps().replicaSets().inNamespace("FunTester").withLabel("foo", "bar").list();
client.apps().replicaSets().inNamespace("FunTester").withName("rs1").delete();
client.apps().replicaSets().inNamespace("FunTester").watch(new Watcher<>() {
    @Override public void eventReceived(Action action, ReplicaSet resource) { /* handle */ }
    @Override public void onClose(WatcherException e) { }
});
client.apps().replicaSets().inNamespace("FunTester").withName("nginx-rs").scale(3);
client.apps().replicaSets().inNamespace("FunTester").withName("soaktestrs").updateImage("nickchase/soaktest");
Map
containerToImageMap = new HashMap<>();
containerToImageMap.put("c1", "image1");
containerToImageMap.put("c2", "image2");
client.apps().replicaSets().inNamespace("FunTester").withName("soaktestrs").updateImage(containerToImageMap);

Show You Code

The following script puts the previous concepts together: it creates a namespace, deploys an Nginx pod, creates a LoadBalancer service, waits for the pod to become ready, prints its logs, and finally deletes the namespace and all resources.

import io.fabric8.kubernetes.api.model.*;
import io.fabric8.kubernetes.client.*;
import io.fabric8.kubernetes.client.dsl.LogWatch;
import io.fabric8.kubernetes.client.dsl.PodResource;
import java.util.concurrent.TimeUnit;

public class KubernetesFunTesterDemo {
    public static void main(String[] args) {
        // Initialize Kubernetes client
        try (KubernetesClient client = new KubernetesClientBuilder().build()) {
            String namespace = "fun-tester";
            // 1. Create namespace
            Namespace ns = new NamespaceBuilder()
                .withNewMetadata().withName(namespace).endMetadata()
                .build();
            client.namespaces().resource(ns).create();
            System.out.println("命名空间 " + namespace + " 创建成功！");
            // 2. Deploy Nginx Pod
            Pod nginxPod = new PodBuilder()
                .withNewMetadata().withName("nginx-pod").addToLabels("app", "nginx").endMetadata()
                .withNewSpec()
                .addNewContainer().withName("nginx-container").withImage("nginx:1.21.0")
                .addNewPort().withContainerPort(80).endPort()
                .endContainer()
                .endSpec()
                .build();
            client.pods().inNamespace(namespace).resource(nginxPod).create();
            System.out.println("Nginx Pod 创建成功！");
            // 3. Create Service
            Service nginxService = new ServiceBuilder()
                .withNewMetadata().withName("nginx-service").endMetadata()
                .withNewSpec()
                .addNewPort().withPort(80).withTargetPort(new IntOrString(80)).endPort()
                .withSelector(nginxPod.getMetadata().getLabels())
                .withType("LoadBalancer")
                .endSpec()
                .build();
            client.services().inNamespace(namespace).resource(nginxService).create();
            System.out.println("Nginx Service 创建成功！");
            // 4. Wait for Pod ready
            PodResource
podResource = client.pods().inNamespace(namespace).withName("nginx-pod");
            Pod readyPod = podResource.waitUntilReady(5, TimeUnit.MINUTES);
            System.out.println("Nginx Pod 已准备就绪，状态为: " + readyPod.getStatus().getPhase());
            // 5. Get Pod logs
            String podLog = podResource.getLog();
            System.out.println("Nginx Pod 日志如下：");
            System.out.println(podLog);
            // 6. Cleanup
            client.namespaces().withName(namespace).delete();
            System.out.println("命名空间 " + namespace + " 及其所有资源已删除！");
        } catch (KubernetesClientException e) {
            System.err.println("Kubernetes 操作失败: " + e.getMessage());
            e.printStackTrace();
        }
    }
}

Notes

Ensure a local Kubernetes cluster (Minikube, Kind, etc.) is running and kubectl works.

If the cluster does not support LoadBalancer , change the Service type to NodePort .

The wait timeout (5 minutes) can be adjusted based on your environment.