Allow optional endpoint argument

Most AWS including ElastiCache allows
customers to invoke APIs using FIPS
endpoint.

https://docs.aws.amazon.com/general/latest/gr/rande.html#FIPS-endpoints

This commit introduces ability to specify
endpoint URL like AWS CLI.

Author: nmvk

pkg/config/config.go

@@ -15,6 +15,7 @@ package config
 
 import (
 	"errors"
+	"net/url"
 
 	flag "github.com/spf13/pflag"
 	"go.uber.org/zap/zapcore"
@@ -29,6 +30,7 @@ const (
 	flagEnableDevLogging     = "enable-development-logging"
 	flagAWSAccountID         = "aws-account-id"
 	flagAWSRegion            = "aws-region"
+	flagAWSEndpointURL       = "aws-endpoint-url"
 	flagLogLevel             = "log-level"
 	flagResourceTags         = "resource-tags"
 )
@@ -41,6 +43,7 @@ type Config struct {
 	EnableDevelopmentLogging bool
 	AccountID                string
 	Region                   string
+	EndpointURL              string
 	LogLevel                 string
 	ResourceTags             []string
 }
@@ -79,6 +82,13 @@ func (cfg *Config) BindFlags() {
 		"",
 		"The AWS Region in which the service controller will create its resources",
 	)
+	flag.StringVar(
+		&cfg.EndpointURL, flagAWSEndpointURL,
+		"",
+		"The AWS endpoint URL the service controller will use to create its resources. This is an optional" +
+			" flag that can be used to override the default behaviour of aws-sdk-go that constructs endpoint URLs" +
+			" automatically based on service and region",
+	)
 	flag.StringVar(
 		&cfg.LogLevel, flagLogLevel,
 		"info",
@@ -117,5 +127,13 @@ func (cfg *Config) Validate() error {
 	if cfg.Region == "" {
 		return errors.New("unable to start service controller as AWS region is nil. Please pass --aws-region flag")
 	}
+
+	if cfg.EndpointURL != "" {
+		endpoint, err := url.Parse(cfg.EndpointURL)
+		if err != nil || endpoint.Scheme != "https" && endpoint.Host != "" {
+			return errors.New("invalid service endpoint. Please refer to " +
+				"https://docs.aws.amazon.com/general/latest/gr/aws-service-information.html for more details")
+		}
+	}
 	return nil
 }

pkg/runtime/reconciler.go

@@ -143,7 +143,7 @@ func (r *reconciler) reconcile(req ctrlrt.Request) error {
 	region := r.getRegion(res)
 	roleARN := r.getRoleARN(acctID)
 	sess, err := r.sc.newSession(
-		region, roleARN,
+		region, &r.cfg.EndpointURL, roleARN,
 		res.RuntimeObject().GetObjectKind().GroupVersionKind(),
 	)
 	if err != nil {

pkg/runtime/session.go

@@ -34,13 +34,18 @@ const appName = "aws-controller-k8s"
 // the session.
 func (c *ServiceController) newSession(
 	region ackv1alpha1.AWSRegion,
+	endpointURL *string,
 	assumeRoleARN ackv1alpha1.AWSResourceName,
 	groupVersionKind schema.GroupVersionKind,
 ) (*session.Session, error) {
 	awsCfg := aws.Config{
 		Region:              aws.String(string(region)),
 		STSRegionalEndpoint: endpoints.RegionalSTSEndpoint,
 	}
+	if endpointURL != nil {
+		awsCfg.Endpoint = endpointURL
+	}
+
 	sess, err := session.NewSession(&awsCfg)
 	if err != nil {
 		return nil, err