Kubernetes & OpenShift Java Client

This client provides access to the full Kubernetes & OpenShift REST APIs via a fluent DSL.

Module	Maven Central	Javadoc
kubernetes-client
openshift-client

Extensions	Maven Central	Javadoc
knative-client
tekton-client
chaosmesh-client
volumesnapshot-client
volcano-client
istio-client
open-cluster-management-client

Contents

• Usage
  • Creating a client
  • Configuring the client
  • Loading resources from external sources
  • Passing a reference of a resource to the client
  • Adapting a client
    • Adapting and close
• Generating CRD from Java
• Generating Java from CRD
• Mocking Kubernetes
• Who Uses Fabric8 Kubernetes Client?
• Kubernetes Operators in Java Written using Fabric8 Kubernetes Client
• Kubernetes and Red Hat OpenShift Compatibility

Usage

Creating a client

The easiest way to create a client is:

KubernetesClient client = new KubernetesClientBuilder().build();

DefaultOpenShiftClient implements both the KubernetesClient & OpenShiftClient interface so if you need the OpenShift extensions, such as Builds, etc then simply do:

OpenShiftClient osClient = new KubernetesClientBuilder().build().adapt(OpenShiftClient.class);

Configuring the client

This will use settings from different sources in the following order of priority:

• System properties
• Environment variables
• Kube config file
• Service account token & mounted CA certificate

System properties are preferred over environment variables. The following system properties & environment variables can be used for configuration:

Property / Environment Variable	Description	Default value
kubernetes.disable.autoConfig / KUBERNETES_DISABLE_AUTOCONFIG	Disable automatic configuration (KubernetesClient would not look in ~/.kube/config, mounted ServiceAccount, environment variables or System properties for Kubernetes cluster information)	false
kubernetes.master / KUBERNETES_MASTER	Kubernetes master URL	https://kubernetes.default.svc
kubernetes.api.version / KUBERNETES_API_VERSION	API version	v1
openshift.url / OPENSHIFT_URL	OpenShift master URL	Kubernetes master URL value
kubernetes.oapi.version / KUBERNETES_OAPI_VERSION	OpenShift API version	v1
kubernetes.trust.certificates / KUBERNETES_TRUST_CERTIFICATES	Trust all certificates	false
kubernetes.disable.hostname.verification / KUBERNETES_DISABLE_HOSTNAME_VERIFICATION		false
kubernetes.certs.ca.file / KUBERNETES_CERTS_CA_FILE
kubernetes.certs.ca.data / KUBERNETES_CERTS_CA_DATA
kubernetes.certs.client.file / KUBERNETES_CERTS_CLIENT_FILE
kubernetes.certs.client.data / KUBERNETES_CERTS_CLIENT_DATA
kubernetes.certs.client.key.file / KUBERNETES_CERTS_CLIENT_KEY_FILE
kubernetes.certs.client.key.data / KUBERNETES_CERTS_CLIENT_KEY_DATA
kubernetes.certs.client.key.algo / KUBERNETES_CERTS_CLIENT_KEY_ALGO	Client key encryption algorithm	RSA

Alternatively you can use the ConfigBuilder to create a config object for the Kubernetes client:

Config config = new ConfigBuilder().withMasterUrl("https://mymaster.com").build();
KubernetesClient client = new KubernetesClientBuilder().withConfig(config).build();

Using the DSL is the same for all resources.

List resources:

NamespaceList myNs = client.namespaces().list();

ServiceList myServices = client.services().list();

ServiceList myNsServices = client.services().inNamespace("default").list();

Get a resource:

Namespace myns = client.namespaces().withName("myns").get();

Service myservice = client.services().inNamespace("default").withName("myservice").get();

Delete:

Namespace myns = client.namespaces().withName("myns").delete();

Service myservice = client.services().inNamespace("default").withName("myservice").delete();

Editing resources uses the inline builders from the Kubernetes Model:

Namespace myns = client.namespaces().withName("myns").edit(n -> new NamespaceBuilder(n)
                   .editMetadata()
                     .addToLabels("a", "label")
                   .endMetadata()
                   .build());

Service myservice = client.services().inNamespace("default").withName("myservice").edit(s -> new ServiceBuilder(s)
                     .editMetadata()
                       .addToLabels("another", "label")
                     .endMetadata()
                     .build());

In the same spirit you can inline builders to create:

Namespace myns = client.namespaces().create(new NamespaceBuilder()
                   .withNewMetadata()
                     .withName("myns")
                     .addToLabels("a", "label")
                   .endMetadata()
                   .build());

Service myservice = client.services().inNamespace("default").create(new ServiceBuilder()
                     .withNewMetadata()
                       .withName("myservice")
                       .addToLabels("another", "label")
                     .endMetadata()
                     .build());

You can also set the apiVersion of the resource like in the case of SecurityContextConstraints :

SecurityContextConstraints scc = new SecurityContextConstraintsBuilder()
		.withApiVersion("v1")
		.withNewMetadata().withName("scc").endMetadata()
		.withAllowPrivilegedContainer(true)
		.withNewRunAsUser()
		.withType("RunAsAny")
		.endRunAsUser()
		.build();

Following events

Use io.fabric8.kubernetes.api.model.Event as T for Watcher:

client.events().inAnyNamespace().watch(new Watcher<>() {

  @Override
  public void eventReceived(Action action, Event resource) {
    System.out.println("event " + action.name() + " " + resource.toString());
  }

  @Override
  public void onClose(WatcherException cause) {
    System.out.println("Watcher close due to " + cause);
  }

});

Working with extensions

The kubernetes API defines a bunch of extensions like daemonSets, jobs, ingresses and so forth which are all usable in the extensions() DSL:

e.g. to list the jobs...

jobs = client.batch().jobs().list();

Loading resources from external sources

There are cases where you want to read a resource from an external source, rather than defining it using the clients DSL. For those cases the client allows you to load the resource from:

• A file (Supports both java.io.File and java.lang.String)
• A url
• An input stream

Once the resource is loaded, you can treat it as you would, had you created it yourself.

For example lets read a pod, from a yml file and work with it:

Pod refreshed = client.load('/path/to/a/pod.yml').fromServer().get();
client.load('/workspace/pod.yml').delete();
LogWatch handle = client.load('/workspace/pod.yml').watchLog(System.out);

Passing a reference of a resource to the client

In the same spirit you can use an object created externally (either a reference or using its string representation).

For example:

Pod pod = someThirdPartyCodeThatCreatesAPod();
client.resource(pod).delete();

Adapting the client

The client supports plug-able adapters. An example adapter is the OpenShift Adapter which allows adapting an existing KubernetesClient instance to an OpenShiftClient one.

For example:

KubernetesClient client = new KubernetesClientBuilder().build();

OpenShiftClient oClient = client.adapt(OpenShiftClient.class);

The client also support the isAdaptable() method which checks if the adaptation is possible and returns true if it does.

KubernetesClient client = new KubernetesClientBuilder().build();
if (client.isAdaptable(OpenShiftClient.class)) {
    OpenShiftClient oClient = client.adapt(OpenShiftClient.class);
} else {
    throw new Exception("Adapting to OpenShiftClient not support. Check if adapter is present, and that env provides /oapi root path.");
}

Adapting and close

Note that when using adapt() both the adaptee and the target will share the same resources (underlying http client, thread pools etc). This means that close() is not required to be used on every single instance created via adapt. Calling close() on any of the adapt() managed instances or the original instance, will properly clean up all the resources and thus none of the instances will be usable any longer.

Mocking Kubernetes

Along with the client this project also provides a Kubernetes Mock Server that you can use for testing purposes.

The Mock Web Server has two modes of operation:

• Expectations mode
• CRUD mode

Expectations mode

In this mode, you can set up expectations for the server to respond to HTTP and websocket requests.

This mode has been extensively used for testing the client itself. Make sure you check kubernetes-test.

To add a Kubernetes server to your test:

@EnableKubernetesMockClient
class MyTestSuite {
  KubernetesMockServer server;
}

Then you can use the server to define the expectations and the client to perform the regular kubernetes operations:

class MyTestSuite {
  KubernetesMockServer server;
  KubernetesClient client;

  @Test
  void myTest() {
    server.expect().get()
      .withPath("/api/v1/namespaces/my-namespace/pods/my-pod")
      .andReturn(200, new PodBuilder().build())
      .always();
    Pod pod = client.pods().inNamespace("my-namespace").withName("my-pod").get();
  }
}

CRUD mode

Defining every single request and response can become tiresome. Given that in most cases the Mock Server is mostly used to perform simple CRUD based operations, a CRUD mode is also available.

When using the CRUD mode, the mock web server will store, read, update and delete kubernetes resources using an in memory map and will appear as a real API server.

To add a Kubernetes Server in crud mode to your test:

@EnableKubernetesMockClient(crud = true)
class MyTestSuite {
  KubernetesClient client;
}

Then you can use the client to perform the regular kubernetes operations:

class MyTestSuite {
  KubernetesClient client;

  @Test
  public void myCrudTest() {
    //CREATE
    client.pods().inNamespace("ns1").create(new PodBuilder().withNewMetadata().withName("pod1").endMetadata().build());

    //READ
    podList = client.pods().inNamespace("ns1").list();
    assertNotNull(podList);
    assertEquals(1, podList.getItems().size());
  }
}

Testing Against real Kubernetes API Server with Kube API Test

In order to test against real Kubernetes API the project provides a lightweight approach, thus starting up Kubernetes API Server and etcd binaries.

@EnableKubeAPIServer
class KubeAPITestSample {

  static KubernetesClient client;
  
  @Test
  void testWithClient() {
    // test using the client against real K8S API Server   
  }
}

For details see docs for Kube API Test.

Compatibility

Kubernetes

Starting from v5.5, the Kubernetes Client should be compatible with any supported Kubernetes cluster version. We provide DSL methods (for example client.pods(), client.namespaces(), and so on) for the most commonly used Kubernetes resources. If the resource you're looking for is not available through the DSL, you can always use the generic client.resource() method to interact with it. You can also open a new issue to request the addition of a new resource to the DSL.

We provide Kubernetes Java model types (for example Pod) and their corresponding builders (for example PodBuilder) for every vanilla Kubernetes resource (and some extensions). If you don't find a specific resource, and you think that it should be part of the Kubernetes Client, please open a new issue.

OpenShift

Starting from v5.5, the OpenShift Client should be compatible with any OpenShift cluster version currently supported by Red Hat. The Fabric8 Kubernetes Client is one of the few Kubernetes Java clients that provides full support for any supported OpenShift cluster version. If you find any incompatibility or something missing, please open a new issue.

Major Changes in Kubernetes Client 4.0.0

All the resource objects used here will be according to OpenShift 3.9.0 and Kubernetes 1.9.0. All the resource objects will give all the fields according to OpenShift 3.9.0 and Kubernetes 1.9.0

• SecurityContextConstraints has been moved to OpenShift client from Kubernetes Client
• Job dsl is in both batch and extensions(Extensions is deprecated)
• DaemonSet dsl is in both apps and extensions(Extensions is deprecated)
• Deployment dsl is in both apps and extensions(Extensions is deprecated)
• ReplicaSet dsl is in both apps and extensions(Extensions is deprecated)
• NetworkPolicy dsl is in both network and extensions(Extensions is deprecated)
• Storage Class moved from client base DSL to storage DSL
• PodSecurityPolicies moved from client base DSL and extensions to only extensions
• ThirdPartyResource has been removed.

Who uses Kubernetes & OpenShift Java client?

Extensions:

• Knative
• Tekton
• Volcano
• Istio
• Open Cluster Management
• Camel-k - Maven Central

Frameworks/Libraries/Tools:

• Arquillian Cube
• Apache Camel
• Apache Flink
• Apache Spark
• Jaeger Kubernetes
• Loom
• Microsoft Azure Libraries for Java
• Spinnaker Halyard
• Spring Cloud Connectors for Kubernetes
• Spring Cloud Kubernetes

CI Plugins:

• Deployment Pipeline Plugin (Jenkins)
• Kubernetes Elastic Agent (GoCD)
• Kubernetes Plugin (Jenkins)
• Kubernetes Pipeline Plugin (Jenkins)
• OpenShift Sync Plugin (Jenkins)
• Kubernetes Plugin (Teamcity from Jetbrains)
• Kubernetes Agents for Bamboo (WindTunnel Technologies)

Build Tools:

• Fabric8 Maven Plugin
• Eclipse JKube
• Gradle Kubernetes Plugin

Platforms:

• Apache Openwhisk
• Eclipse che
• Openshift.io (Launcher service)
• Spotify Styx
• Strimzi
• Syndesis
• StackGres
• Boomerang Flow
• Apache Kyuubi

Proprietary Platforms:

• vCommander

As our community grows, we would like to track keep track of our users. Please send a PR with your organization/community name.

Tests we run for every new Pull Request

There are the links of the Github Actions and Jenkins for the tests which run for every new Pull Request. You can view all the recent builds also.

• Regression Tests
• Unit Tests

To get the updates about the releases, you can join https://groups.google.com/forum/embed/?place=forum/fabric8-devclients

Kubectl Java Equivalents

This table provides kubectl to Kubernetes Java Client mappings. Most of the mappings are quite straightforward and are one liner operations. However, some might require slightly more code to achieve same result:

kubectl	Fabric8 Kubernetes Client
kubectl config view	ConfigViewEquivalent.java
kubectl config get-contexts	ConfigGetContextsEquivalent.java
kubectl config current-context	ConfigGetCurrentContextEquivalent.java
kubectl config use-context minikube	ConfigUseContext.java
kubectl config view -o jsonpath='{.users[*].name}'	ConfigGetCurrentContextEquivalent.java
kubectl get pods --all-namespaces	PodListGlobalEquivalent.java
kubectl get pods	PodListEquivalent.java
kubectl get pods -w	PodWatchEquivalent.java