`list_namespaced_pod()` should accept `label_selector` values of `dict` type

[volkert-fastned]

What happened (please include outputs or screenshots):

I did a lot of searching on-line, and I couldn't find a trivial way to obtain a list of pods belonging to a certain service.

What I understand is that services are associated with their corresponding pods by the selector labels they have in common.

So what I tried to do is obtain the selector from read_namespaced_service() and then passing that selector on as the label_selector argument to list_namespaced_pod().

That resulted in the following error:

kubernetes.client.exceptions.ApiException: (400)
Reason: Bad Request

The response also contained HTTP response headers and a HTTP response body with error messages that made it clear that it choked on special characters in the dict, which apparently got rendered as a JSON object, instead of the expected comma-separated a=b,x=y selector labels notation.

What you expected to happen:

I would expect this to work, and see the list of pods corresponding to service myapp.

How to reproduce it (as minimally and precisely as possible):

So first, I look up the service (assuming service/application name myapp), for which I want to retrieve the corresponding pods:

from kubernetes import client, config

config.load_kube_config()
v1 = client.CoreV1Api()
myapp_svc = v1.read_namespaced_service(namespace="myappnamespace", name="myapp")
print(myapp_svc.spec.selector)

At this point, myapp_svc.spec.selector contains a dict with the label selector keys and their corresponding values.

So subsequently, I want to look up the corresponding pods:

ret = v1.list_namespaced_pod(namespace="myappnamespace",
                             label_selector=myapp_svc.spec.selector)
for i in ret.items:
    print(i.metadata.name)

Anything else we need to know?:

I found a workaround in this answer on StackOverflow, which dates back to 2018, but still works. But this is an awkward and unintuitive workaround. Why does the API expect us to perform such a conversion manually? Or better yet, would it perhaps be possible to add a list_service_pods() function to the API that simply takes a reference to the service retrieved from read_namespaced_service() and returns the corresponding pods?

Also, maybe there is a far more trivial and more proper way to solve this problem, but honestly, I haven't been able to find such a solution on-line. If so, could you maybe clarify this in the documentation, or perhaps add an example to the examples folder in this project?

This issue is similar, but not entirely identical to issue #1559. That issue was about not being able to pass on a selector obtained from V1LabelSelector to list_namespaced_pod(), which resulted in the same problem. That issue was closed without a proper resolution.

Thank you kindly for looking into this.

Environment:

• Python client version (pip list | grep kubernetes): 25.3.0

[Ananya2001-an]

Hey @volkert-fastned the label selector param should be something like this: app=value so you have to do something like this to make it work:

ret = v1.list_namespaced_pod(namespace="default",
                             label_selector="app=" + myapp_svc.spec.selector["app"])

[roycaihw]

/assign @Ananya2001-an Thank you!

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@k8s-triage-robot: Closing this issue, marking it as "Not Planned".

In response to this:

The Kubernetes project currently lacks enough active contributors to adequately respond to all issues and PRs.

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/close not-planned

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