Added getting region from ARN prefix if missing from AWS SDK configuration

Author: olgierdg

arnutil/arnutil.go

@@ -28,6 +28,16 @@ func ValidateARN(arnString string) bool {
 	return true
 }
 
+// Helper function to get region from ARNs
+func GetRegionFromARN(arnString string) string {
+	arn, err := arn.Parse(arnString)
+	if err != nil {
+		log.Warnf("The ARN supplied as argument does not parse successfully: %s", arnString)
+		return ""
+	}
+	return arn.Region
+}
+
 // InstanceProfileArn uses the EC2 metadata API to find the role for
 // the instance.
 func InstanceProfileArn(svc *ec2metadata.EC2Metadata) (arn.ARN, error) {

main.go

@@ -118,6 +118,13 @@ func main() {
 		}),
 	)
 
+	// if region is not configured according to AWS SDK docs, but ARN prefix is provided
+	// the region will be parsed from the ARN prefix
+	if config.Region == nil && *arnPrefix != "" {
+		arnRegion := arnutil.GetRegionFromARN(*arnPrefix)
+		config.Region = &arnRegion
+	}
+
 	session, err := session.NewSessionWithOptions(session.Options{
 		Config: *config,
 	})