javakuberneteskubernetes-java-client

The Java client of kubernetes retrieves the 'status. phase' of the pod for Terminating status, which is' Running '

I am a newcomer to Kubernetes and I would like to know if there are better attributes to accurately describe the state of pod

Kubernetes version: Kubernetes v1.27.3
java client maven:
<dependency>
    <groupId>io.kubernetes</groupId>
    <artifactId>client-java</artifactId>
    <version>18.0.1</version>
</dependency>

I am conducting testing in a Kubernetes cluster with two nodes. I am shutting down the Kubelet service on the slave node to simulate a loss of connectivity from the slave node, allowing the pod of the slave node to be automatically scheduled to the master node

When I use the following command:

kubectl get po -n my-namespace -o wide

we can see

nginx1-74499f547c-gbdzf                     1/1     Running       0              6h10m   10.244.0.55   kylin-master     <none>           <none>
nginx1-74499f547c-xndkm                     1/1     Terminating   0              8h      10.244.2.24   kylin-worker02   <none>           <none>

Obviously, the status of nginx1-74499f547c-xndkm is Terminating

But when I use the following code to retrieve the pod and traverse it to find a pod with the same name

CoreV1Api coreV1Api = new CoreV1Api();
V1PodList v1PodList;
try{
    v1PodList = coreV1Api.listNamespacedPod(tenxOpenApiConfig.getTeamSpace(), null, null, null, info, null, null, null, null, null, null);
    for (V1Pod item : v1PodList.getItems()) {
       // .....
    }
} 
// ......

enter image description here

The name of pod is nginx1-74499f547c-xndkm, but item.status.phase="Running" .

I can't understand why this is happening, is it a bug? Still, status.phase is not suitable for representing pod status.

Looking forward to your help.

Solution

  • TL;dr
    Kubernetes Pods and containers doesn't have Terminating as status, and kubectl prints the status based on multiple fields in the Pod object to be more concise (not just pod.status.phase, like pod.metadata.deletionTimestamp). Let me explain below in more details.

    More details
    When a pod is being deleted for any reason (e.g. Node failure or manual deletion), it doesn't happen immediately as it could be disruptive to the application running inside, so kubernetes gives a TERM(aka. SIGTERM) signal to the containers inside the pod first to give it some time to terminate gracefully. After some time (defined in pod.spec.terminationGracePeriodSeconds, defaults to 30) if the containers aren't terminated yet, it kills them. During this period, containers are actually running, so that's why kubernetes reports the containers and the pods as running. However, when the pod is being deleted, kubernetes sets pod.metadata.deletionTimestamp to the time the delete was issued.
    Kubectl is smart enough to detect this and show the status of Pod as Terminating when it sees this.

    Documentation
    There is a nice documentation about this here.

    Let me highlight a useful paragraph:

    Note: When a Pod is being deleted, it is shown as Terminating by some kubectl commands. This Terminating status is not one of the Pod phases. A Pod is granted a term to terminate gracefully, which defaults to 30 seconds. You can use the flag --force to terminate a Pod by force.

    Additional advice
    You can see the pod mostly* as you see it in the code by using -o yaml. Example:

    kubectl get pod -n my-namespace -o yaml

    Hope this helps :)