How to do "patchNamespacedPod" using AppsV1Api

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Hi All,

Hoping someone can shed a bit of light on this (newbie alert):
I am trying to get into k8s to use for a stateful solution (two pods, one active, one standby). I have been following this example (Active/Passive Kubernetes deployment for HA mission-critical stateful applications | Medium) as template.

One thing it does, is to use the k8s API to modify the value of a label, from inside the pod, using something like this (in JS):

const patch = {
    op: 'replace',
    path: '/metadata/labels/mode',
    value: "some value"
};


const options = { headers: { 'Content-type': k8s.PatchUtils.PATCH_FORMAT_JSON_PATCH} };
ksApi.patchNamespacedPod(HOSTNAME, 'default', [patch], undefined, undefined, undefined, undefined, options)

I need to work in Java, so I tried to replicate this using the official Java Client (V24), like this:

String jsonPatchStr =
        "[{\"op\":\"replace\",\"path\":\"/metadata/labels/mode\",\"value\":\"some value\"}]";

CoreV1Api k8sApi = new CoreV1Api();
String podName = System.getenv("HOSTNAME");
k8sApi.patchNamespacedPod(podName, "default", body);

this does not work as there is no way (that I could find) to specify that the patch is PATCH_FORMAT_JSON_PATCH.

OK, so I looked at PachUtils, and got this far:

String jsonPatchStr =
        "[{\"op\":\"replace\",\"path\":\"/metadata/labels/mode\",\"value\":\"some value\"}]";
AppsV1Api api = new AppsV1Api(ClientBuilder.standard().build());
V1Deployment deploy2 =
        PatchUtils.patch(
                V1Deployment.class,
                () -> api.patchNamespacedDeployment(
                                "k8s-test-app",//cannot specify pod here?,
                                "default",
                                new V1Patch(jsonPatchStr))
                        .buildCall(null),
                V1Patch.PATCH_FORMAT_JSON_PATCH,
                k8sApi.getApiClient());

And this works, but only sets the attribute in the deployment (as the api patchNamespacedDeployment() suggests). So yeah, but not what I need. I was unable to find any way to patch a specific pod with AppsV1Api

With CoreV1Api I can address a specific pod, but cannot specify PATCH_FORMAT_JSON_PATCH.
With AppsV1Api I can specify PATCH_FORMAT_JSON_PATCH, but cannot specify the pod.

Am I barking up the wrong tree (i.e. “don’t/you can’t do that”), or am I missing something here?

Cluster information: Minikube
Kubernetes version: Client Version: v1.34.1, Kustomize Version: v5.7.1, Server Version: v1.34.0
Cloud being used: bare-metal
Installation method: directly installed on WLS with apt
Host OS: WSL on W11

My app.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: k8s-test-app
  labels:
    app: k8s-test
spec:
  replicas: 1
  selector:
    matchLabels:
      app: k8s-test
  template:
    metadata:
      labels:
        app: k8s-test
        mode: unknown
    spec:
      containers:
      - name: k8s-test
        image: k8s-test-app
        imagePullPolicy: Never
        ports:
        - containerPort: 80

My rbac.yaml:

kind: Role
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  namespace: default
  name: update-pods
rules:
  - apiGroups: ["*"] # "" indicates the core API group
    resources: ["apps", "deployments", "pods"]
    verbs: ["get", "delete", "list", "patch"]
---
kind: RoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: update-pods-rb
subjects:
  - kind: ServiceAccount
    name: default
    namespace: default
roleRef:
  kind: Role
  name: update-pods
  apiGroup: ""