Using Java Kubernetes Clients to Perform CRUD Operations on Config Map Resources.

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In this blog post we will look at how we can use the fabric 8’s Kubernetes client for java and official Kubernetes client for java to retrieve, create, update and delete a config map resource type.

Using Fabric 8’s Kubernetes Client

Configuring the client

This client can be configured using System properties, environment variables, a kubeconfig file, and service account token & mounted CA certificate. The properties that can be configured using properties and environment variables can be found here.

In order to perform CRUD operations we need to first create a client.

var client = new DefaultKubernetesClient();

We will use the following two variables to store the namespace (aka virtual cluster — the default namespace is “default”) which contains the config map resource and the name of the config map resource.

var namespace = "default";
var name = "CONFIGMAP_NAME";

Creating a Config Map Resource.

var configMapResource = client.configMaps()
    .inNamespace(namespace)
    .withName(name);
var configMap = configMapResource.createOrReplace(new ConfigMapBuilder().
          withNewMetadata().withName(name).endMetadata().
          addToData("key", "value").
          build());

Retrieve a Config Map Resource

var configMap = client.configMaps()
    .inNamespace(NAMESPACE)
    .withName(name)
    .get().

Updating a Config Map Resource

client.configMaps().inNamespace(namespace).withName(name)
.edit(
  c -> new ConfigMapBuilder(c).addToData("NEW_KEY","NEW_VALUE")
       .build()
);

Deleting a Config Map Resource

client.configMaps().inNamespace(namespace).withName(name)
           .delete();

Using the Official Kubernetes Java client

We can perform the same operations easily using the official kubernetes API client for java. It also has a similar fluent API to the one in fabric 8 client, in addition to being more flexible.

Configuring the client

Since we are using the standard client builder, it can be configured as follows (in the order of priority),

• If $KUBECONFIG is defined, use that config file.
• If $HOME/.kube/config can be found, use that.
• If the in-cluster service account can be found, assume in cluster config.
• Default to localhost:8080 as a last resort.

If we are not using the standard client builder, we can use the kubeconfig builder as follows.

var kubeConfigPath = "<path-to-kube-config-file">
var apiClient = ClientBuilder
    .kubeconfig(KubeConfig.loadKubeConfig(
        new FileReader(kubeConfigPath)
    )).build();

Creating a Config Map

The following code demonstrates how the fluent api can be used to create a new config map.

var apiClient = ClientBuilder.standard().build();
var api = new CoreV1Api(apiClient);    
       
var configMap = new V1ConfigMapBuilder()
        .withNewMetadata()
        .withName(name)
        .endMetadata()
        .addToData("KEY", "VALUE")
        .build();
api.createNamespacedConfigMap(
    namespace,
    name, 
    null, null, null);

Retrieve a Config Map Resource

var apiClient = ClientBuilder.standard().build();                                      var api = new CoreV1Api(apiClient);
var configMapClient = new GenericKubernetesApi<>(
    V1ConfigMap.class,                                                  
    V1ConfigMapList.class, "", "v1", "configmaps", 
    apiClient
);   
var response = configMapClient.get(namespace, namespace);                                      var configmap = response.getObject();

Editing a Config Map Resource

There are different ways to do this. Here I will show how to update a config map using JSON patch as it allows granular updates.

var apiClient = ClientBuilder.standard().build();
var api = new CoreV1Api(apiClient);
var jsonPatchStr = "[{
    \"op\" : \"replace\", 
    \"path\":\"/data/KEY\", 
    \"value\": \"CHANGED\"
}]";
var configMap = PatchUtils.patch(
    V1ConfigMap.class,
    () ->  api.patchNamespacedConfigMapCall(
             name,
             namespace,
             new V1Patch(jsonPatchStr),
             null,
             null,
             null, 
             null,
             null),
    V1Patch.PATCH_FORMAT_JSON_PATCH,
    api.getApiClient()   
);

This will update the config map’s “KEY” key with the value “CHANGED”.

Deleting a Config Map using name

var apiClient = ClientBuilder.standard().build();
var api = new CoreV1Api(apiClient);
api.deleteNamespacedConfigMap(
    "<config-map-name-here>", 
    "<namespace-here>", 
    null, null, null, null, null, null);

You can learn more about these two libraries by going to their GitHub repositories linked below.

Resources

kubernetes-client/java

fabric8io/kubernetes-client