Access Clusters Using the Kubernetes API

    You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

    To check the version, enter .

    When accessing the Kubernetes API for the first time, use the Kubernetes command-line tool, kubectl.

    To access a cluster, you need to know the location of the cluster and have credentials to access it. Typically, this is automatically set-up when you work through a , or someone else setup the cluster and provided you with credentials and a location.

    Check the location and credentials that kubectl knows about with this command:

    Many of the examples provide an introduction to using kubectl. Complete documentation is found in the .

    kubectl handles locating and authenticating to the API server. If you want to directly access the REST API with an http client like curl or wget, or a browser, there are multiple ways you can locate and authenticate against the API server:

    1. Run kubectl in proxy mode (recommended). This method is recommended, since it uses the stored apiserver location and verifies the identity of the API server using a self-signed cert. No man-in-the-middle (MITM) attack is possible using this method.
    2. Alternatively, you can provide the location and credentials directly to the http client. This works with client code that is confused by proxies. To protect against man in the middle attacks, you’ll need to import a root cert into your browser.

    Using the Go or Python client libraries provides accessing kubectl in proxy mode.

    Using kubectl proxy

    The following command runs kubectl in a mode where it acts as a reverse proxy. It handles locating the API server and authenticating.

    Run it like this:

    1. kubectl proxy --port=8080 &

    Then you can explore the API with curl, wget, or a browser, like so:

    1. curl http://localhost:8080/api/

    The output is similar to this:

    1. {
    2.   "versions": [
    3.     "v1"
    4.   ],
    5.   "serverAddressByClientCIDRs": [
    6.     {
    7.       "clientCIDR": "0.0.0.0/0",
    8.       "serverAddress": "10.0.1.149:443"
    9.     }
    10.   ]
    11. }

    Without kubectl proxy

    It is possible to avoid using kubectl proxy by passing an authentication token directly to the API server, like this:

    Using grep/cut approach:

    The output is similar to this:

    1. {
    2.   "kind": "APIVersions",
    3.   "versions": [
    4.     "v1"
    5.   ],
    6.   "serverAddressByClientCIDRs": [
    7.     {
    8.       "clientCIDR": "0.0.0.0/0",
    9.       "serverAddress": "10.0.1.149:443"
    10.     }
    11.   ]
    12. }

    Using jsonpath approach:

    1. APISERVER=$(kubectl config view --minify -o jsonpath='{.clusters[0].cluster.server}')
    2. TOKEN=$(kubectl get secret $(kubectl get serviceaccount default -o jsonpath='{.secrets[0].name}') -o jsonpath='{.data.token}' | base64 --decode )
    3. curl $APISERVER/api --header "Authorization: Bearer $TOKEN" --insecure
    4. {
    5.   "kind": "APIVersions",
    6.   "versions": [
    7.     "v1"
    8.   ],
    9.   "serverAddressByClientCIDRs": [
    10.     {
    11.       "clientCIDR": "0.0.0.0/0",
    12.     }
    13.   ]
    14. }

    The above example uses the --insecure flag. This leaves it subject to MITM attacks. When kubectl accesses the cluster it uses a stored root certificate and client certificates to access the server. (These are installed in the ~/.kube directory). Since cluster certificates are typically self-signed, it may take special configuration to get your http client to use root certificate.

    On some clusters, the API server does not require authentication; it may serve on localhost, or be protected by a firewall. There is not a standard for this. Controlling Access to the Kubernetes API describes how you can configure this as a cluster administrator.

    Kubernetes officially supports client libraries for , Python, , dotnet, , and Haskell. There are other client libraries that are provided and maintained by their authors, not the Kubernetes team. See for accessing the API from other languages and how they authenticate.

    Go client

    • To get the library, run the following command: go get k8s.io/client-go@kubernetes-<kubernetes-version-number> See to see which versions are supported.
    • Write an application atop of the client-go clients.

    Note: client-go defines its own API objects, so if needed, import API definitions from client-go rather than from the main repository. For example, import "k8s.io/client-go/kubernetes" is correct.

    1. package main
    4.   "context"
    5.   "fmt"
    6.   "k8s.io/apimachinery/pkg/apis/meta/v1"
    7.   "k8s.io/client-go/kubernetes"
    8.   "k8s.io/client-go/tools/clientcmd"
    9. )
    11. func main() {
    12.   // uses the current context in kubeconfig
    13.   // path-to-kubeconfig -- for example, /root/.kube/config
    14.   config, _ := clientcmd.BuildConfigFromFlags("", "<path-to-kubeconfig>")
    15.   // creates the clientset
    16.   clientset, _ := kubernetes.NewForConfig(config)
    17.   // access the API to list pods
    18.   pods, _ := clientset.CoreV1().Pods("").List(context.TODO(), v1.ListOptions{})
    19.   fmt.Printf("There are %d pods in the cluster\n", len(pods.Items))
    20. }

    If the application is deployed as a Pod in the cluster, see Accessing the API from within a Pod.

    Python client

    To use Python client, run the following command: pip install kubernetes See for more installation options.

    The Python client can use the same kubeconfig file as the kubectl CLI does to locate and authenticate to the API server. See this :

    Java client

    To install the , run:

    1. # Clone java library
    2. git clone --recursive https://github.com/kubernetes-client/java
    4. # Installing project artifacts, POM etc:
    5. cd java
    6. mvn install

    See https://github.com/kubernetes-client/java/releases to see which versions are supported.

    The Java client can use the same as the kubectl CLI does to locate and authenticate to the API server. See this example:

    1. package io.kubernetes.client.examples;
    3. import io.kubernetes.client.ApiClient;
    4. import io.kubernetes.client.ApiException;
    5. import io.kubernetes.client.Configuration;
    6. import io.kubernetes.client.apis.CoreV1Api;
    7. import io.kubernetes.client.models.V1Pod;
    8. import io.kubernetes.client.models.V1PodList;
    9. import io.kubernetes.client.util.ClientBuilder;
    10. import io.kubernetes.client.util.KubeConfig;
    11. import java.io.FileReader;
    12. import java.io.IOException;
    14. /**
    15.  * A simple example of how to use the Java API from an application outside a kubernetes cluster
    16.  *
    17.  * <p>Easiest way to run this: mvn exec:java
    18.  * -Dexec.mainClass="io.kubernetes.client.examples.KubeConfigFileClientExample"
    19.  *
    20.  */
    21. public class KubeConfigFileClientExample {
    22.   public static void main(String[] args) throws IOException, ApiException {
    24.     String kubeConfigPath = "~/.kube/config";
    26.     // loading the out-of-cluster config, a kubeconfig from file-system
    28.         ClientBuilder.kubeconfig(KubeConfig.loadKubeConfig(new FileReader(kubeConfigPath))).build();
    30.     // set the global default api-client to the in-cluster one from above
    31.     Configuration.setDefaultApiClient(client);
    33.     // the CoreV1Api loads default api-client from global configuration.
    34.     CoreV1Api api = new CoreV1Api();
    36.     // invokes the CoreV1Api client
    37.     V1PodList list = api.listPodForAllNamespaces(null, null, null, null, null, null, null, null, null);
    38.     System.out.println("Listing all pods: ");
    39.     for (V1Pod item : list.getItems()) {
    40.       System.out.println(item.getMetadata().getName());
    41.     }
    42.   }
    43. }

    dotnet client

    To use dotnet client, run the following command: dotnet add package KubernetesClient --version 1.6.1 See for more installation options. See https://github.com/kubernetes-client/csharp/releases to see which versions are supported.

    The dotnet client can use the same as the kubectl CLI does to locate and authenticate to the API server. See this example:

    1. using System;
    2. using k8s;
    4. namespace simple
    5. {
    6.     internal class PodList
    7.     {
    8.         private static void Main(string[] args)
    9.         {
    10.             var config = KubernetesClientConfiguration.BuildDefaultConfig();
    11.             IKubernetes client = new Kubernetes(config);
    12.             Console.WriteLine("Starting Request!");
    14.             var list = client.ListNamespacedPod("default");
    15.             foreach (var item in list.Items)
    16.             {
    17.                 Console.WriteLine(item.Metadata.Name);
    18.             }
    19.             if (list.Items.Count == 0)
    20.             {
    21.                 Console.WriteLine("Empty!");
    22.             }
    23.         }
    24.     }
    25. }

    JavaScript client

    To install JavaScript client, run the following command: npm install @kubernetes/client-node. See to see which versions are supported.

    The JavaScript client can use the same kubeconfig file as the kubectl CLI does to locate and authenticate to the API server. See this :

    Haskell client

    The can use the same kubeconfig file as the kubectl CLI does to locate and authenticate to the API server. See this :

    1. exampleWithKubeConfig :: IO ()
    2. exampleWithKubeConfig = do
    3.     oidcCache <- atomically $ newTVar $ Map.fromList []
    4.     (mgr, kcfg) <- mkKubeClientConfig oidcCache $ KubeConfigFile "/path/to/kubeconfig"
    5.     dispatchMime
    6.             mgr
    7.             kcfg
    8.             (CoreV1.listPodForAllNamespaces (Accept MimeJSON))