[kubenetes] Lookup k8s API endpoint using environment variables

[rosskukulinski]

From: #2551

The Kubernetes integration finds the kubernetes api using DNS which is not always available. Specifically, not all namespaces will have the kubernetes service running (e.g. kube-system).

The preferred mechanism to get the API server host/port is by using the environmental variables injected into every pod: KUBERNETES_SERVICE_HOST and KUBERNETES_SERVICE_PORT.

Relevant code: https://github.com/DataDog/dd-agent/blob/master/utils/kubeutil.py#L66

[onbjerg]

I'll take this when #2728 is merged.

[xvello]

Hello,

5.14 uses KUBERNETES_SERVICE_HOST, and 5.15 will also use KUBERNETES_SERVICE_PORT, plus configurable host and port for the apiserver (see
#3401)

Regards