Upstream client support for eno reconciler (#33)

Eno reconciler accepts an optional path to an upstream client through
the "remote-kubeconfig" flag.

cmd/eno-reconciler/main.go

@@ -12,6 +12,7 @@ import (
 	ctrl "sigs.k8s.io/controller-runtime"
 
 	"github.com/Azure/eno/internal/controllers/reconciliation"
+	"github.com/Azure/eno/internal/k8s"
 	"github.com/Azure/eno/internal/manager"
 	"github.com/Azure/eno/internal/reconstitution"
 )
@@ -32,6 +33,8 @@ func run() error {
 		writeBatchInterval     time.Duration
 		discoveryMaxRPS        float32
 		debugLogging           bool
+		remoteKubeconfigFile   string
+		remoteQPS              float64
 
 		mgrOpts = &manager.Options{
 			Rest: ctrl.GetConfigOrDie(),
@@ -40,6 +43,8 @@ func run() error {
 	flag.BoolVar(&rediscoverWhenNotFound, "rediscover-when-not-found", true, "Invalidate discovery cache when any type is not found in the openapi spec. Set this to false on <= k8s 1.14")
 	flag.DurationVar(&writeBatchInterval, "write-batch-interval", time.Second*5, "The max throughput of composition status updates")
 	flag.BoolVar(&debugLogging, "debug", true, "Enable debug logging")
+	flag.StringVar(&remoteKubeconfigFile, "remote-kubeconfig", "", "Path to the kubeconfig of the apiserver where the resources will be reconciled. The config from the environment is used if this is not provided")
+	flag.Float64Var(&remoteQPS, "remote-qps", 0, "Max requests per second to the remote apiserver")
 	mgrOpts.Bind(flag.CommandLine)
 	flag.Parse()
 
@@ -63,7 +68,16 @@ func run() error {
 		return fmt.Errorf("constructing reconstitution manager: %w", err)
 	}
 
-	err = reconciliation.New(recmgr, mgr.GetConfig(), discoveryMaxRPS, rediscoverWhenNotFound)
+	remoteConfig := mgr.GetConfig()
+	if remoteKubeconfigFile != "" {
+		if remoteConfig, err = k8s.GetRESTConfig(remoteKubeconfigFile); err != nil {
+			return err
+		}
+		if remoteQPS != 0 {
+			remoteConfig.QPS = float32(remoteQPS)
+		}
+	}
+	err = reconciliation.New(recmgr, remoteConfig, discoveryMaxRPS, rediscoverWhenNotFound)
 	if err != nil {
 		return fmt.Errorf("constructing reconciliation controller: %w", err)
 	}

internal/k8s/kubeconfig.go

@@ -0,0 +1,22 @@
+package k8s
+
+import (
+	"fmt"
+	"os"
+
+	"k8s.io/client-go/rest"
+	"k8s.io/client-go/tools/clientcmd"
+)
+
+// GetRESTConfig is a convenience method to avoid manually opening a file.
+func GetRESTConfig(filename string) (*rest.Config, error) {
+	b, err := os.ReadFile(filename)
+	if err != nil {
+		return nil, fmt.Errorf("could not get read Kubeconfig file: %w", err)
+	}
+	cfg, err := clientcmd.RESTConfigFromKubeConfig(b)
+	if err != nil {
+		return nil, fmt.Errorf("could not get get Kubeconfig from file: %w", err)
+	}
+	return cfg, nil
+}