[exporter/datadog] Kubernetes node name resolution via the downward API

[mx-psi]

Is your feature request related to a problem? Please describe.

The Datadog exporter needs to query the Kubernetes node name for resolving the hostname (see #10911). The exporter currently relies on the assumption that the pod name can be retrieved by calling os.Hostname, which is not necessarily true if, e.g., the hostname has been modified via fields like setHostnameAsFQDN. In these cases, the Kubernetes source provider will fail.

Describe the solution you'd like

The Datadog exporter Kubernetes source provider supports getting the node name via the downward API or directly from the known environment variables documented in open-telemetry/oteps#195.

Describe alternatives you've considered

There are no alternatives to support these setups, really.

Additional context

Originally mentioned in #10911 (comment)

[github-actions]

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Pinging code owners:

• exporter/datadog: @KSerrania @mx-psi @gbbr @knusbaum @amenasria @dineshg13

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[github-actions]

This issue has been inactive for 60 days. It will be closed in 60 days if there is no activity. To ping code owners by adding a component label, see Adding Labels via Comments, or if you are unsure of which component this issue relates to, please ping @open-telemetry/collector-contrib-triagers. If this issue is still relevant, please ping the code owners or leave a comment explaining why it is still relevant. Otherwise, please close it.

Pinging code owners:

• exporter/datadog: @KSerrania @mx-psi @gbbr @knusbaum @amenasria @dineshg13

See Adding Labels via Comments if you do not have permissions to add labels yourself.

[ringerc]

This should use the downward API to inject both the k8s pod name and the node name into the Pod at DaemonSet level

spec:
  template:
    spec:
      containers:
        - name: opentelemetry-collector
          env:
          - name: K8S_POD_IP
            valueFrom:
              fieldRef:
                fieldPath: status.podIP
          - name: K8S_NODE_NAME
            valueFrom:
              fieldRef:
                fieldPath: spec.nodeName
          - name: K8S_NAMESPACE_NAME
            valueFrom:
              fieldRef:
                fieldPath: metadata.namespace
          ...

... but preferably adjusted to follow OpenTelemetry semantic conventions for resource environment variables.

The current code at

opentelemetry-collector-contrib/exporter/datadogexporter/internal/hostmetadata/internal/k8s/nodename.go

Lines 39 to 57 in 2c29c26

	func (p *nodeNameProviderImpl) NodeName(ctx context.Context) (string, error) {
	namespace := p.namespace()
	// NOTE: The pod name may not match the OS hostname, e.g. if it has been modified
	// via the 'setHostnameAsFQDN' and 'hostname' fields in the pod spec.
	// The query below will error out in that case. See:
	// https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/11033
	podName, err := os.Hostname()
	if err != nil {
	return "", fmt.Errorf("could not fetch pod hostname: %w", err)
	}
	// NOTE: If changing this, check if the RBAC rules on the docs or examples need updates.
	pod, err := p.client.CoreV1().Pods(namespace).Get(ctx, podName, metav1.GetOptions{})
	if err != nil {
	return "", err
	}
	return pod.Spec.NodeName, nil
	}

relies on the assumption that hostname within a pod returns the pod name, which as the comments say isn't always guaranteed.