external-dns/pkg/client/config.go

/*
Copyright 2026 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

// Package kubeclient provides shared utilities for creating Kubernetes REST configurations
// and clients with standardized metrics instrumentation.
package kubeclient

import (
	"os"
	"time"

	log "github.com/sirupsen/logrus"
	"k8s.io/client-go/kubernetes"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/tools/clientcmd"

	extdnshttp "sigs.k8s.io/external-dns/pkg/http"
)

// GetRestConfig returns the REST client configuration for Kubernetes API access.
// Supports both in-cluster and external cluster configurations.
//
// Configuration Priority:
// 1. KubeConfig file if specified
// 2. Recommended home file (~/.kube/config)
// 3. In-cluster config
// TODO: consider clientcmd.NewDefaultClientConfigLoadingRules() with clientcmd.NewNonInteractiveDeferredLoadingClientConfig
func GetRestConfig(kubeConfig, apiServerURL string) (*rest.Config, error) {
	if kubeConfig == "" {
		if _, err := os.Stat(clientcmd.RecommendedHomeFile); err == nil {
			kubeConfig = clientcmd.RecommendedHomeFile
		}
	}
	log.Debugf("apiServerURL: %s", apiServerURL)
	log.Debugf("kubeConfig: %s", kubeConfig)

	// evaluate whether to use kubeConfig-file or serviceaccount-token
	var (
		config *rest.Config
		err    error
	)
	if kubeConfig == "" {
		log.Debug("Using inCluster-config based on serviceaccount-token")
		config, err = rest.InClusterConfig()
	} else {
		log.Debug("Using kubeConfig")
		config, err = clientcmd.BuildConfigFromFlags(apiServerURL, kubeConfig)
	}
	if err != nil {
		return nil, err
	}

	return config, nil
}

// InstrumentedRESTConfig creates a REST config with request instrumentation for monitoring.
// Adds HTTP transport wrapper for Prometheus metrics collection and request timeout configuration.
//
// Metrics: Wraps the transport with pkg/http.NewInstrumentedTransport to collect
// HTTP request duration metrics for all Kubernetes API calls.
//
// Timeout: Applies the specified request timeout to prevent hanging requests.
func InstrumentedRESTConfig(kubeConfig, apiServerURL string, requestTimeout time.Duration) (*rest.Config, error) {
	config, err := GetRestConfig(kubeConfig, apiServerURL)
	if err != nil {
		return nil, err
	}

	config.WrapTransport = extdnshttp.NewInstrumentedTransport
	config.Timeout = requestTimeout

	return config, nil
}

// NewKubeClient returns a new Kubernetes client object. It takes a Config and
// uses APIServerURL and KubeConfig attributes to connect to the cluster. If
// KubeConfig isn't provided it defaults to using the recommended default.
func NewKubeClient(kubeConfig, apiServerURL string, requestTimeout time.Duration) (*kubernetes.Clientset, error) {
	log.Infof("Instantiating new Kubernetes client")
	config, err := InstrumentedRESTConfig(kubeConfig, apiServerURL, requestTimeout)
	if err != nil {
		return nil, err
	}
	client, err := kubernetes.NewForConfig(config)
	if err != nil {
		return nil, err
	}
	log.Infof("Created Kubernetes client %s", config.Host)
	return client, nil
}