Why does the Python Kubernetes Client fail with exec-based authentication while kubectl succeeds?

Below is a list of suggestions to help debug your Python client authorization issue:

1. Verify Python Client Version

Ensure you are using a recent version of the Kubernetes Python client. Support for exec-based authentication has evolved over time, so it’s important that your client version supports the exec plugin configuration in your kubeconfig file. You can check your version with:

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pip show kubernetes

And update if necessary:

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pip install --upgrade kubernetes

2. Confirm Exec Plugin Output Format

Your kubeconfig uses the exec credential plugin (your custom token generator). The Python client expects the plugin output in a specific JSON format. Verify that your custom command (./mycustom_token_generator_cmd) returns a valid JSON with the expected fields, such as "status" and "token". (Note that kubectl uses the same plugin without issues, so comparing outputs might help.)

3. Check That the Exec Plugin Is Invoked

Since using the kubeconfig with kubectl works, the difference may be that the Python client is not invoking your exec plugin properly. You can try adding some temporary logging inside your token generator (if possible) to see when it is called. Additionally, you may increase verbosity in your Python client logging:

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import logging
logging.basicConfig(level=logging.DEBUG)

Place this at the very start of your script to capture more detailed debugging output.

4. Validate the Kubeconfig Context and Fields

Double-check that the context (mycluster-context), user (mycluster-user), and the associated exec configuration in your kubeconfig are correctly defined and that there are no typos or missing/incorrect fields. Although kubectl might be less strict, the Python client may fail if, for example, the apiVersion in the exec section isn’t what the Python client expects.

5. Handle Token Refresh or Caching Issues

If your token generator returns an expired or invalid token, the API server will reject the request with a 401 error. Confirm that your token generator returns a fresh token every time it’s invoked. The Python client may cache tokens differently from kubectl if the token output contains an expiration time.

6. Test Direct Authentication

As a temporary workaround, try generating a token manually using your custom command and then populating the configuration programmatically. This can help isolate whether the issue is with the exec plugin handling inside the Python client. For instance:

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import subprocess
import json
from kubernetes import client, configuration

# Run your token generator command and parse the output
token_output = subprocess.check_output(["./mycustom_token_generator_cmd", "token_gen_args"])
token_data = json.loads(token_output)
token = token_data.get("status", {}).get("token")

# Create a configuration object manually
configuration = client.Configuration()
configuration.host = "https://<mycluster IP>:443"
configuration.verify_ssl = True
configuration.api_key = {"authorization": "Bearer " + token}
# Configure certificate-authority if needed
configuration.ssl_ca_cert = "/path/to/your/ca_cert"

client.Configuration.set_default(configuration)
v1 = client.CoreV1Api()
ret = v1.list_pod_for_all_namespaces(watch=False)
print(ret)

This manual approach can help confirm that your API server and token are correct.

Summary

To debug the issue, begin by ensuring that your Python client’s version fully supports exec-based authentication and that your custom token generator returns the expected JSON format. Then, verify logging to see if your exec plugin is being called and consider manually setting the token to isolate the problem. This step-by-step approach should help you narrow down the authorization issue.

If the problem persists, you might also check the Kubernetes GitHub issues for the Python client to see if others have similar problems with exec credentials.