Listening for pod fail in kubernetes java client?

Question

i'm new to kubernetes i need to write a program that is listening to kubernetes change such as new pod creation or pod deletion. For these i've already the solution but i don't know how to listen for failing of pods, can someone help? I'm using the kubernetes java official client but i can also switch to another language to solve the problem, Thanks

Answer 1

You can check the pod status, here you have some examples into https://github.com/kubernetes-client/java

You can take this example to get the pod status:

import io.kubernetes.client.openapi.ApiClient;
import io.kubernetes.client.openapi.ApiException;
import io.kubernetes.client.openapi.Configuration;
import io.kubernetes.client.openapi.apis.CoreV1Api;
import io.kubernetes.client.openapi.models.V1Pod;
import io.kubernetes.client.openapi.models.V1PodList;
import io.kubernetes.client.util.Config;

import java.io.IOException;

public class Example {
    public static void main(String[] args) throws IOException, ApiException{
        ApiClient client = Config.defaultClient();
        Configuration.setDefaultApiClient(client);

        CoreV1Api api = new CoreV1Api();
        V1PodList list = api.listPodForAllNamespaces(null, null, null, null, null, null, null, null, null);
        for (V1Pod item : list.getItems()) {
            System.out.println(item.getMetadata().getName());
            System.out.println(item.getStatus());
        }
    }
}

Also you can watch:

import com.google.gson.reflect.TypeToken;
import io.kubernetes.client.openapi.ApiClient;
import io.kubernetes.client.openapi.ApiException;
import io.kubernetes.client.openapi.Configuration;
import io.kubernetes.client.openapi.apis.CoreV1Api;
import io.kubernetes.client.openapi.models.V1Namespace;
import io.kubernetes.client.util.Config;
import io.kubernetes.client.util.Watch;

import java.io.IOException;

public class WatchExample {
    public static void main(String[] args) throws IOException, ApiException{
        ApiClient client = Config.defaultClient();
        Configuration.setDefaultApiClient(client);

        CoreV1Api api = new CoreV1Api();

        Watch<V1Namespace> watch = Watch.createWatch(
                client,
                api.listNamespaceCall(null, null, null, null, null, 5, null, null, Boolean.TRUE, null, null),
                new TypeToken<Watch.Response<V1Namespace>>(){}.getType());

        for (Watch.Response<V1Namespace> item : watch) {
            System.out.printf("%s : %s%n", item.type, item.object.getMetadata().getName());
        }
    }
}

Answer 2

As previously mentioned by the user Ruben, we can implement a watch. To go even beyond, I have provided an example on how to run health checks too. The following block of code is merely the watch event with the pod status in the MODIFIED case.

try (Watch<V1Pod> watch = Watch.createWatch(
        client,
        coreV1Api.listNamespacedPodCall(namespace, null, null, null, null,
                labels, null, null, null, null, Boolean.TRUE, null),
        new TypeToken<Watch.Response<V1Pod>>() {
        }.getType())) {

    for (Watch.Response<V1Pod> eventPod : watch) {
        V1Pod pod = eventPod.object;
        switch (eventPod.type) {
            case "ADDED":
                System.out.println("Pod: " + pod.getMetadata().getName() + " ADDED\n");
                break;
            case "MODIFIED":
                System.out.println("Pod: " + pod.getMetadata().getName() + " has been MODIFIED\n");
                // Check to see the current status of the pod
                if (!pod.getStatus().getPhase().equals("Running")){
                    System.out.println("Pod: " + pod.getMetadata.getName() + " is now " + pod.getStatus());
                }
                break;
            case "DELETED":
                System.out.println("Pod: " + pod.getMetadata().getName() + " has been DELETED\n");
            default:
                System.out.println("Unknown Event Occurred: " + eventPod.type + "\n");
        }
    }
} catch (Exception e) {
    System.out.println("Error: " + e.getMessage());
}

Kubernetes defines the different statuses that you could implement as part of the health check condition.