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Kubernetes Client

Quarkus includes the kubernetes-client extension which enables the use of the Fabric8 Kubernetes Client in native mode while also making it easier to work with.

Having a Kubernetes Client extension in Quarkus is very useful in order to unlock the power of Kubernetes Operators. Kubernetes Operators are quickly emerging as a new class of Cloud Native applications. These applications essentially watch the Kubernetes API and react to changes on various resources and can be used to manage the lifecycle of all kinds of complex systems like databases, messaging systems and much more. Being able to write such operators in Java with the very low footprint that native images provide is a great match.

Configuración

Once you have your Quarkus project configured you can add the kubernetes-client extension to your project by running the following command in your project base directory.

CLI
quarkus extension add kubernetes-client
Maven
./mvnw quarkus:add-extension -Dextensions='kubernetes-client'
Gradle
./gradlew addExtension --extensions='kubernetes-client'

Esto añadirá lo siguiente a su archivo de construcción:

pom.xml
<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-kubernetes-client</artifactId>
</dependency>
build.gradle
implementation("io.quarkus:quarkus-kubernetes-client")

Uso

Quarkus configures a Bean of type KubernetesClient which can be injected into application code using the well known CDI methods. This client can be configured using various properties as can be seen in the following example:

quarkus.kubernetes-client.trust-certs=false
quarkus.kubernetes-client.namespace=default

Note that the full list of properties is available in the Dev Services section of the configuration reference.

In dev mode and when running tests, Dev Services for Kubernetes automatically starts a Kubernetes API server.

Customizing and overriding

Quarkus provides multiple integration points for influencing the Kubernetes Client provided as a CDI bean.

Kubernetes Client Config customization

The first integration point is the use of the io.quarkus.kubernetes.client.KubernetesConfigCustomizer interface. When such a bean exists, it allows for arbitrary customizations of the io.fabric8.kubernetes.client.Config created by Quarkus (which takes into account the quarkus.kubernetes-client.* properties).

Alternatively, application code can override the io.fabric8.kubernetes.client.Config or even the io.fabric8.kubernetes.client.KubernetesClient bean (which are normally provided by the extension) by simply declaring custom versions of those beans.

An example of this can be seen in the following snippet:

@Singleton
public class KubernetesClientProducer {

    @Produces
    public KubernetesClient kubernetesClient() {
        // here you would create a custom client
        return new DefaultKubernetesClient();
    }
}

Kubernetes Client ObjectMapper customization

The Fabric8 Kubernetes Client uses its own ObjectMapper instance for serialization and deserialization of Kubernetes resources. This mapper is provided to the client through a KubernetesSerialization instance that’s injected into the KubernetesClient bean.

If for some reason you must customize the default ObjectMapper bean provided by this extension and used by the Kubernetes Client, you can do so by declaring a bean that implements the KubernetesClientObjectMapperCustomizer interface.

The following code snippet contains an example of a KubernetesClientObjectMapperCustomizer to set the ObjectMapper locale:

@Singleton
public static class Customizer implements KubernetesClientObjectMapperCustomizer {
    @Override
    public void customize(ObjectMapper objectMapper) {
        objectMapper.setLocale(Locale.ROOT);
    }
}

Furthermore, if you must replace the default ObjectMapper bean used by the Kubernetes Client that the extension creates automatically, you can do so by declaring a bean of type @KubernetesClientObjectMapper. The following code snippet shows how you can declare this bean:

@Singleton
public class KubernetesObjectMapperProducer {
    @KubernetesClientObjectMapper
    @Singleton
    @Produces
    public ObjectMapper kubernetesClientObjectMapper() {
        return new ObjectMapper();
    }
}
The static io.fabric8.kubernetes.client.utils.Serialization utils class is deprecated and should not be used. Access to Serialization.jsonMapper() should be replaced by the usage of @KubernetesClientObjectMapperCustomizer` declared beans.

Probando

To make testing against a mock Kubernetes API extremely simple, Quarkus provides the WithKubernetesTestServer annotation which automatically launches a mock of the Kubernetes API server and sets the proper environment variables needed so that the Kubernetes Client configures itself to use said mock. Tests can inject the mock server and set it up in any way necessary for the particular testing using the @KubernetesTestServer annotation.

Let’s assume we have a REST endpoint defined like so:

@Path("/pod")
public class Pods {

    private final KubernetesClient kubernetesClient;

    public Pods(KubernetesClient kubernetesClient) {
        this.kubernetesClient = kubernetesClient;
    }

    @GET
    @Path("/{namespace}")
    public List<Pod> pods(String namespace) {
        return kubernetesClient.pods().inNamespace(namespace).list().getItems();
    }
}

We could write a test for this endpoint very easily like so:

// you can even configure aspects like crud, https and port on this annotation
@WithKubernetesTestServer
@QuarkusTest
public class KubernetesClientTest {

    @KubernetesTestServer
    KubernetesServer mockServer;
    @Inject
    KubernetesClient client;

    @BeforeEach
    public void before() {
        final Pod pod1 = new PodBuilder().withNewMetadata().withName("pod1").withNamespace("test").and().build();
        final Pod pod2 = new PodBuilder().withNewMetadata().withName("pod2").withNamespace("test").and().build();

        // Set up Kubernetes so that our "pretend" pods are created
        client.pods().resource(pod1).create();
        client.pods().resource(pod2).create();
    }

    @Test
    public void testInteractionWithAPIServer() {
        RestAssured.when().get("/pod/test").then()
                .body("size()", is(2));
    }

}

Note that to take advantage of these features, the quarkus-test-kubernetes-client dependency needs to be added, for example like so:

pom.xml
<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-test-kubernetes-client</artifactId>
    <scope>test</scope>
</dependency>
build.gradle
testImplementation("io.quarkus:quarkus-test-kubernetes-client")

By default, the mock server will be in CRUD mode, so you have to use the client to build your state before your application can retrieve it, but you can also set it up in non-CRUD mode and mock all HTTP requests made to Kubernetes:

// you can even configure aspects like crud, https and port on this annotation
@WithKubernetesTestServer(crud = false)
@QuarkusTest
public class KubernetesClientTest {

    @KubernetesTestServer
    KubernetesServer mockServer;

    @BeforeEach
    public void before() {
        final Pod pod1 = new PodBuilder().withNewMetadata().withName("pod1").withNamespace("test").and().build();
        final Pod pod2 = new PodBuilder().withNewMetadata().withName("pod2").withNamespace("test").and().build();

        // Mock any HTTP request to Kubernetes pods so that our pods are returned
        mockServer.expect().get().withPath("/api/v1/namespaces/test/pods")
                .andReturn(200,
                        new PodListBuilder().withNewMetadata().withResourceVersion("1").endMetadata().withItems(pod1, pod2)
                                .build())
                .always();
    }

    @Test
    public void testInteractionWithAPIServer() {
        RestAssured.when().get("/pod/test").then()
                .body("size()", is(2));
    }

}

You can also use the setup attribute on the @WithKubernetesTestServer annotation to provide a class that will configure the KubernetesServer instance:

@WithKubernetesTestServer(setup = MyTest.Setup.class)
@QuarkusTest
public class MyTest {

    public static class Setup implements Consumer<KubernetesServer> {

        @Override
        public void accept(KubernetesServer server) {
          server.expect().get().withPath("/api/v1/namespaces/test/pods")
            .andReturn(200, new PodList()).always();
        }
    }

    // tests
}

Alternately, you can create an extension of the KubernetesServerTestResource class to ensure all your @QuarkusTest enabled test classes share the same mock server setup via the QuarkusTestResource annotation:

public class CustomKubernetesMockServerTestResource extends KubernetesServerTestResource {

    @Override
    protected void configureServer() {
        super.configureServer();
        server.expect().get().withPath("/api/v1/namespaces/test/pods")
          .andReturn(200, new PodList()).always();
    }
}

and use this in your other test classes as follows:

@QuarkusTestResource(CustomKubernetesMockServerTestResource.class)
@QuarkusTest
public class KubernetesClientTest {

    //tests will now use the configured server...
}

Note on implementing or extending generic types

Due to the restrictions imposed by GraalVM, extra care needs to be taken when implementing or extending generic types provided by the client if the application is intended to work in native mode. Essentially every implementation or extension of generic classes such as Watcher, ResourceHandler or CustomResource needs to specify their associated Kubernetes model class (or, in the case of CustomResource, regular Java types) at class definition time. To better understand this, suppose we want to watch for changes to Kubernetes Pod resources. There are a couple ways to write such a Watcher that are guaranteed to work in native:

client.pods().watch(new Watcher<Pod>() {
    @Override
    public void eventReceived(Action action, Pod pod) {
        // do something
    }

    @Override
    public void onClose(KubernetesClientException e) {
        // do something
    }
});

or

public class PodResourceWatcher implements Watcher<Pod> {
    @Override
    public void eventReceived(Action action, Pod pod) {
        // do something
    }

    @Override
    public void onClose(KubernetesClientException e) {
        // do something
    }
}

...


client.pods().watch(new PodResourceWatcher());

Note that defining the generic type via a class hierarchy similar to the following example will also work correctly:

public abstract class MyWatcher<S> implements Watcher<S> {
}

...


client.pods().watch(new MyWatcher<Pod>() {
    @Override
    public void eventReceived(Action action, Pod pod) {
        // do something
    }
});
The following example will not work in native mode because the generic type of watcher cannot be determined by looking at the class and method definitions thus making Quarkus unable to properly determine the Kubernetes model class for which reflection registration is needed:
public class ResourceWatcher<T extends HasMetadata> implements Watcher<T> {
    @Override
    public void eventReceived(Action action, T resource) {
        // do something
    }

    @Override
    public void onClose(KubernetesClientException e) {
        // do something
    }
}

client.pods().watch(new ResourceWatcher<Pod>());

Note on using Elliptic Curve keys

Please note that if you would like to use Elliptic Curve keys with Kubernetes Client then adding a BouncyCastle PKIX dependency is required:

pom.xml
<dependency>
    <groupId>org.bouncycastle</groupId>
    <artifactId>bcpkix-jdk18on</artifactId>
</dependency>
build.gradle
implementation("org.bouncycastle:bcpkix-jdk18on")

Note that internally an org.bouncycastle.jce.provider.BouncyCastleProvider provider will be registered if it has not already been registered.

You can have this provider registered as described in the BouncyCastle or BouncyCastle FIPS sections.

Access to the Kubernetes API

In many cases in order to access the Kubernetes API server a ServiceAccount, Role and RoleBinding will be necessary. An example that allows listing all pods could look something like this:

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: <applicationName>
  namespace: <namespace>
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: <applicationName>
  namespace: <namespace>
rules:
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: <applicationName>
  namespace: <namespace>
roleRef:
  kind: Role
  name: <applicationName>
  apiGroup: rbac.authorization.k8s.io
subjects:
  - kind: ServiceAccount
    name: <applicationName>
    namespace: <namespace>

Replace <applicationName> and <namespace> with your values. Have a look at Configure Service Accounts for Pods to get further information.

OpenShift Client

If the targeted Kubernetes cluster is an OpenShift cluster, it is possible to access it through the openshift-client extension, in a similar way. This leverages the dedicated fabric8 openshift client, and provides access to OpenShift proprietary objects (e.g. Route, ProjectRequest, BuildConfig …​)

Note that the configuration properties are shared with the kubernetes-client extension. In particular, they have the same quarkus.kubernetes-client prefix.

Add the extension with:

CLI
quarkus extension add openshift-client
Maven
./mvnw quarkus:add-extension -Dextensions='openshift-client'
Gradle
./gradlew addExtension --extensions='openshift-client'

Note that openshift-client extension has a dependency on the kubernetes-client extension.

To use the client, inject an OpenShiftClient instead of the KubernetesClient:

@Inject
private OpenShiftClient openshiftClient;

If you need to override the default OpenShiftClient, provide a producer such as:

@Singleton
public class OpenShiftClientProducer {

    @Produces
    public OpenShiftClient openshiftClient() {
        // here you would create a custom client
        return new DefaultOpenShiftClient();
    }
}

Mock support is also provided in a similar fashion:

@QuarkusTestResource(OpenShiftMockServerTestResource.class)
@QuarkusTest
public class OpenShiftClientTest {

    @MockServer
    private OpenShiftMockServer mockServer;
...

Or by using the @WithOpenShiftTestServer similar to the @WithKubernetesTestServer explained in the previous section:

@WithOpenShiftTestServer
@QuarkusTest
public class OpenShiftClientTest {

    @OpenShiftTestServer
    private OpenShiftServer mockOpenShiftServer;
...

To use this feature, you have to add a dependency on quarkus-test-openshift-client:

pom.xml
<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-test-openshift-client</artifactId>
    <scope>test</scope>
</dependency>
build.gradle
testImplementation("io.quarkus:quarkus-test-openshift-client")

Referencia de configuración

Propiedad de configuración fijada en tiempo de compilación - Todas las demás propiedades de configuración son anulables en tiempo de ejecución

Configuration property

Tipo

Por defecto

Whether the client should trust a self-signed certificate if so presented by the API server

Environment variable: QUARKUS_KUBERNETES_CLIENT_TRUST_CERTS

Show more

boolean

URL of the Kubernetes API server

Environment variable: QUARKUS_KUBERNETES_CLIENT_API_SERVER_URL

Show more

string

Default namespace to use

Environment variable: QUARKUS_KUBERNETES_CLIENT_NAMESPACE

Show more

string

CA certificate file

Environment variable: QUARKUS_KUBERNETES_CLIENT_CA_CERT_FILE

Show more

string

CA certificate data

Environment variable: QUARKUS_KUBERNETES_CLIENT_CA_CERT_DATA

Show more

string

Client certificate file

Environment variable: QUARKUS_KUBERNETES_CLIENT_CLIENT_CERT_FILE

Show more

string

Client certificate data

Environment variable: QUARKUS_KUBERNETES_CLIENT_CLIENT_CERT_DATA

Show more

string

Client key file

Environment variable: QUARKUS_KUBERNETES_CLIENT_CLIENT_KEY_FILE

Show more

string

Client key data

Environment variable: QUARKUS_KUBERNETES_CLIENT_CLIENT_KEY_DATA

Show more

string

Client key algorithm

Environment variable: QUARKUS_KUBERNETES_CLIENT_CLIENT_KEY_ALGO

Show more

string

Client key passphrase

Environment variable: QUARKUS_KUBERNETES_CLIENT_CLIENT_KEY_PASSPHRASE

Show more

string

Kubernetes auth username

Environment variable: QUARKUS_KUBERNETES_CLIENT_USERNAME

Show more

string

Kubernetes auth password

Environment variable: QUARKUS_KUBERNETES_CLIENT_PASSWORD

Show more

string

Kubernetes oauth token

Environment variable: QUARKUS_KUBERNETES_CLIENT_TOKEN

Show more

string

Watch reconnect interval

Environment variable: QUARKUS_KUBERNETES_CLIENT_WATCH_RECONNECT_INTERVAL

Show more

Duration 

Maximum reconnect attempts in case of watch failure By default there is no limit to the number of reconnect attempts

Environment variable: QUARKUS_KUBERNETES_CLIENT_WATCH_RECONNECT_LIMIT

Show more

int

Maximum amount of time to wait for a connection with the API server to be established

Environment variable: QUARKUS_KUBERNETES_CLIENT_CONNECTION_TIMEOUT

Show more

Duration 

Maximum amount of time to wait for a request to the API server to be completed

Environment variable: QUARKUS_KUBERNETES_CLIENT_REQUEST_TIMEOUT

Show more

Duration 

Maximum number of retry attempts for API requests that fail with an HTTP code of >= 500

Environment variable: QUARKUS_KUBERNETES_CLIENT_REQUEST_RETRY_BACKOFF_LIMIT

Show more

int

Time interval between retry attempts for API requests that fail with an HTTP code of >= 500

Environment variable: QUARKUS_KUBERNETES_CLIENT_REQUEST_RETRY_BACKOFF_INTERVAL

Show more

Duration 

HTTP proxy used to access the Kubernetes API server

Environment variable: QUARKUS_KUBERNETES_CLIENT_HTTP_PROXY

Show more

string

HTTPS proxy used to access the Kubernetes API server

Environment variable: QUARKUS_KUBERNETES_CLIENT_HTTPS_PROXY

Show more

string

Proxy username

Environment variable: QUARKUS_KUBERNETES_CLIENT_PROXY_USERNAME

Show more

string

Proxy password

Environment variable: QUARKUS_KUBERNETES_CLIENT_PROXY_PASSWORD

Show more

string

IP addresses or hosts to exclude from proxying

Environment variable: QUARKUS_KUBERNETES_CLIENT_NO_PROXY

Show more

list of string

Enable the generation of the RBAC manifests. If enabled and no other role binding are provided using the properties quarkus.kubernetes.rbac., it will generate a default role binding using the role "view" and the application service account.

Environment variable: QUARKUS_KUBERNETES_CLIENT_GENERATE_RBAC

Show more

boolean

true

Dev Services

Tipo

Por defecto

If Dev Services for Kubernetes should be used. (default to true) If this is true and kubernetes client is not configured then a kubernetes cluster will be started and will be used.

Environment variable: QUARKUS_KUBERNETES_CLIENT_DEVSERVICES_ENABLED

Show more

boolean

true

The kubernetes api server version to use. If not set, Dev Services for Kubernetes will use the latest supported version of the given flavor. see https://github.com/dajudge/kindcontainer/blob/master/k8s-versions.json

Environment variable: QUARKUS_KUBERNETES_CLIENT_DEVSERVICES_API_VERSION

Show more

string

The flavor to use (kind, k3s or api-only). Default to api-only.

Environment variable: QUARKUS_KUBERNETES_CLIENT_DEVSERVICES_FLAVOR

Show more

kindkind (needs priviledge docker), k3sk3s (needs priviledge docker), api-onlyapi only

api-onlyapi only

By default, if a kubeconfig is found, Dev Services for Kubernetes will not start. Set this to true to override the kubeconfig config.

Environment variable: QUARKUS_KUBERNETES_CLIENT_DEVSERVICES_OVERRIDE_KUBECONFIG

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boolean

false

Indicates if the Kubernetes cluster managed by Quarkus Dev Services is shared. When shared, Quarkus looks for running containers using label-based service discovery. If a matching container is found, it is used, and so a second one is not started. Otherwise, Dev Services for Kubernetes starts a new container.

The discovery uses the quarkus-dev-service-kubernetes label. The value is configured using the service-name property.

Container sharing is only used in dev mode.

Environment variable: QUARKUS_KUBERNETES_CLIENT_DEVSERVICES_SHARED

Show more

boolean

true

The value of the quarkus-dev-service-kubernetes label attached to the started container. This property is used when shared is set to true. In this case, before starting a container, Dev Services for Kubernetes looks for a container with the quarkus-dev-service-kubernetes label set to the configured value. If found, it will use this container instead of starting a new one. Otherwise, it starts a new container with the quarkus-dev-service-kubernetes label set to the specified value.

This property is used when you need multiple shared Kubernetes clusters.

Environment variable: QUARKUS_KUBERNETES_CLIENT_DEVSERVICES_SERVICE_NAME

Show more

string

kubernetes

Environment variables that are passed to the container.

Environment variable: QUARKUS_KUBERNETES_CLIENT_DEVSERVICES_CONTAINER_ENV__ENVIRONMENT_VARIABLE_NAME_

Show more

Map<String,String>

About the Duration format

To write duration values, use the standard java.time.Duration format. See the Duration#parse() Java API documentation for more information.

You can also use a simplified format, starting with a number:

  • If the value is only a number, it represents time in seconds.

  • If the value is a number followed by ms, it represents time in milliseconds.

In other cases, the simplified format is translated to the java.time.Duration format for parsing:

  • If the value is a number followed by h, m, or s, it is prefixed with PT.

  • If the value is a number followed by d, it is prefixed with P.

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