Infer aws region from eks cluster (#82)

Author: bendu

README.md

@@ -26,7 +26,7 @@ See the demo from AWS Container Day x KubeCon!
 
 First, install the controller with latest release on at least 2 AWS EKS clusters. Nodes must have sufficient IAM permissions to perform CloudMap operations.
 
-> **_NOTE:_** AWS region environment variable should be set like `export AWS_REGION=us-west-2`
+> **_NOTE:_** AWS region environment variable can be _optionaly_ set like `export AWS_REGION=us-west-2` Otherwise controller will infer region in the order `AWS_REGION` environment variable, ~/.aws/config file, then EC2 metadata (for EKS environment)
 
 ```sh
 kubectl apply -k "github.com/aws/aws-cloud-map-mcs-controller-for-k8s/config/controller_install_release"
@@ -74,7 +74,7 @@ kubectl get ServiceImport -A
 
 AWS Cloud Map MCS Controller for K8s adheres to the [SemVer](https://semver.org/) specification. Each release updates the major version tag (eg. `vX`), a major/minor version tag (eg. `vX.Y`) and a major/minor/patch version tag (eg. `vX.Y.Z`). To see a full list of all releases, refer to our [Github releases page](https://github.com/aws/aws-cloud-map-mcs-controller-for-k8s/releases).
 
-> **_NOTE:_** AWS region environment variable should be set like `export AWS_REGION=us-west-2`
+> **_NOTE:_** AWS region environment variable can be _optionally_ set like `export AWS_REGION=us-west-2` Otherwise controller will infer region in the order `AWS_REGION` environment variable, ~/.aws/config file, then EC2 metadata (for EKS environment)
 
 To install from a release run
 ```sh

main.go

@@ -19,10 +19,11 @@ package main
 import (
 	"context"
 	"flag"
+	"os"
+
 	"github.com/aws/aws-cloud-map-mcs-controller-for-k8s/pkg/cloudmap"
 	"github.com/aws/aws-cloud-map-mcs-controller-for-k8s/pkg/version"
 	"github.com/aws/aws-sdk-go-v2/config"
-	"os"
 
 	// Import all Kubernetes client auth plugins (e.g. Azure, GCP, OIDC, etc.)
 	// to ensure that exec-entrypoint and run can make use of them.
@@ -84,18 +85,17 @@ func main() {
 		setupLog.Error(err, "unable to start manager")
 		os.Exit(1)
 	}
+	setupLog.Info("configuring AWS session")
+	// GO sdk will look for region in order 1) AWS_REGION env var, 2) ~/.aws/config file, 3) EC2 IMDS
+	awsCfg, err := config.LoadDefaultConfig(context.TODO(), config.WithEC2IMDSRegion())
 
-	// TODO: configure session
-	awsRegion := os.Getenv("AWS_REGION")
-	setupLog.Info("configuring AWS session", "AWS_REGION", awsRegion)
-	awsCfg, err := config.LoadDefaultConfig(context.TODO(),
-		config.WithRegion(awsRegion),
-	)
-	if err != nil {
-		setupLog.Error(err, "unable to configure AWS session", "AWS_REGION", awsRegion)
+	if err != nil || awsCfg.Region == "" {
+		setupLog.Error(err, "unable to configure AWS session", "AWS_REGION", awsCfg.Region)
 		os.Exit(1)
 	}
 
+	setupLog.Info("Running with AWS region", "AWS_REGION", awsCfg.Region)
+
 	serviceDiscoveryClient := cloudmap.NewDefaultServiceDiscoveryClient(&awsCfg)
 	if err = (&controllers.ServiceExportReconciler{
 		Client:   mgr.GetClient(),