[plugin/route53] Cleanup AWS config/credentials setup. (#5370)

Signed-off-by: Dmitry Ilyevsky <ilyevsky@gmail.com>

plugin/route53/README.md

@@ -9,7 +9,7 @@
 The route53 plugin is useful for serving zones from resource record
 sets in AWS route53. This plugin supports all Amazon Route 53 records
 ([https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/ResourceRecordTypes.html](https://docs.aws.amazon.com/Route53/latest/DeveloperGuide/ResourceRecordTypes.html)).
-The route53 plugin can be used when coredns is deployed on AWS or elsewhere.
+The route53 plugin can be used when CoreDNS is deployed on AWS or elsewhere.
 
 ## Syntax
 
@@ -31,9 +31,9 @@ route53 [ZONE:HOSTED_ZONE_ID...] {
     accessed.
 
 *   **AWS\_ACCESS\_KEY\_ID** and **AWS\_SECRET\_ACCESS\_KEY** the AWS access key ID and secret access key
-    to be used when query AWS (optional). If they are not provided, then coredns tries to access
-    AWS credentials the same way as AWS CLI, e.g., environmental variables, AWS credentials file,
-    instance profile credentials, etc.
+    to be used when querying AWS (optional). If they are not provided, CoreDNS tries to access
+    AWS credentials the same way as AWS CLI - environment variables, shared credential file (and optionally
+    shared config file if `AWS_SDK_LOAD_CONFIG` env is set), and lastly EC2 Instance Roles.
     Note the usage of `aws_access_key` has been deprecated and may be removed in future versions. Instead,
     user can use other methods to pass crentials, e.g., with environmental variable `AWS_ACCESS_KEY_ID` and
     `AWS_SECRET_ACCESS_KEY`, respectively.
@@ -41,9 +41,12 @@ route53 [ZONE:HOSTED_ZONE_ID...] {
 *   `aws_endpoint` can be used to control the endpoint to use when querying AWS (optional). **ENDPOINT** is the
     URL of the endpoint to use. If this is not provided the default AWS endpoint resolution will occur.
 
-*   `credentials` is used for reading the credential **FILENAME** and setting the **PROFILE** name for a given
-    zone. **PROFILE** is the AWS account profile name. Defaults to `default`. **FILENAME** is the
-    AWS credentials filename, defaults to `~/.aws/credentials`.
+*   `credentials` is used for overriding the shared credentials **FILENAME** and the **PROFILE** name for a
+    given zone. **PROFILE** is the AWS account profile name. Defaults to `default`. **FILENAME** is the
+    AWS shared credentials filename, defaults to `~/.aws/credentials`. CoreDNS will only load shared credentials
+    file and not shared config file (`~/.aws/config`) by default. Set `AWS_SDK_LOAD_CONFIG` env variable to
+    a truthy value to enable also loading of `~/.aws/config` (e.g. if you want to provide assumed IAM role
+    configuration). Will be ignored if static keys are set via `aws_access_key`.
 
 *   `fallthrough` If zone matches and no record can be generated, pass request to the next plugin.
     If **ZONES** is omitted, then fallthrough happens for all zones for which the plugin is

plugin/route53/setup.go

@@ -3,6 +3,7 @@ package route53
 import (
 	"context"
 	"fmt"
+	"os"
 	"strconv"
 	"strings"
 	"time"
@@ -26,8 +27,8 @@ var log = clog.NewWithPlugin("route53")
 func init() { plugin.Register("route53", setup) }
 
 // exposed for testing
-var f = func(credential *credentials.Credentials, endpoint *string) route53iface.Route53API {
-	return route53.New(session.Must(session.NewSession(&aws.Config{Credentials: credential, Endpoint: endpoint})))
+var f = func(opts session.Options) route53iface.Route53API {
+	return route53.New(session.Must(session.NewSessionWithOptions(opts)))
 }
 
 func setup(c *caddy.Controller) error {
@@ -35,16 +36,15 @@ func setup(c *caddy.Controller) error {
 		keyPairs := map[string]struct{}{}
 		keys := map[string][]string{}
 
-		// Route53 plugin attempts to find AWS credentials by using ChainCredentials.
-		// And the order of that provider chain is as follows:
-		// Static AWS keys -> Environment Variables -> Credentials file -> IAM role
-		// With that said, even though a user doesn't define any credentials in
-		// Corefile, we should still attempt to read the default credentials file,
-		// ~/.aws/credentials with the default profile.
-		sharedProvider := &credentials.SharedCredentialsProvider{}
-		var providers []credentials.Provider
+		// Route53 plugin attempts to load AWS credentials following default SDK chaining.
+		// The order configuration is loaded in is:
+		// * Static AWS keys set in Corefile (deprecated)
+		// * Environment Variables
+		// * Shared Credentials file
+		// * Shared Configuration file (if AWS_SDK_LOAD_CONFIG is set to truthy value)
+		// * EC2 Instance Metadata (credentials only)
+		opts := session.Options{}
 		var fall fall.F
-		var endpoint string
 
 		refresh := time.Duration(1) * time.Minute // default update frequency to 1 minute
 
@@ -74,16 +74,11 @@ func setup(c *caddy.Controller) error {
 				if len(v) < 2 {
 					return plugin.Error("route53", c.Errf("invalid access key: '%v'", v))
 				}
-				providers = append(providers, &credentials.StaticProvider{
-					Value: credentials.Value{
-						AccessKeyID:     v[0],
-						SecretAccessKey: v[1],
-					},
-				})
+				opts.Config.Credentials = credentials.NewStaticCredentials(v[0], v[1], "")
 				log.Warningf("Save aws_access_key in Corefile has been deprecated, please use other authentication methods instead")
 			case "aws_endpoint":
 				if c.NextArg() {
-					endpoint = c.Val()
+					opts.Config.Endpoint = aws.String(c.Val())
 				} else {
 					return plugin.Error("route53", c.ArgErr())
 				}
@@ -91,12 +86,17 @@ func setup(c *caddy.Controller) error {
 				c.RemainingArgs() // eats args
 			case "credentials":
 				if c.NextArg() {
-					sharedProvider.Profile = c.Val()
+					opts.Profile = c.Val()
 				} else {
 					return c.ArgErr()
 				}
 				if c.NextArg() {
-					sharedProvider.Filename = c.Val()
+					opts.SharedConfigFiles = []string{c.Val()}
+					// If AWS_SDK_LOAD_CONFIG is set also load ~/.aws/config to stay consistent
+					// with default SDK behavior.
+					if ok, _ := strconv.ParseBool(os.Getenv("AWS_SDK_LOAD_CONFIG")); ok {
+						opts.SharedConfigFiles = append(opts.SharedConfigFiles, defaults.SharedConfigFilename())
+					}
 				}
 			case "fallthrough":
 				fall.SetZonesFromArgs(c.RemainingArgs())
@@ -122,13 +122,7 @@ func setup(c *caddy.Controller) error {
 			}
 		}
 
-		session, err := session.NewSession(&aws.Config{})
-		if err != nil {
-			return plugin.Error("route53", err)
-		}
-
-		providers = append(providers, &credentials.EnvProvider{}, sharedProvider, defaults.RemoteCredProvider(*session.Config, session.Handlers))
-		client := f(credentials.NewChainCredentials(providers), &endpoint)
+		client := f(opts)
 		ctx, cancel := context.WithCancel(context.Background())
 		h, err := New(ctx, client, keys, refresh)
 		if err != nil {

plugin/route53/setup_test.go

@@ -5,12 +5,12 @@ import (
 
 	"github.com/coredns/caddy"
 
-	"github.com/aws/aws-sdk-go/aws/credentials"
+	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/aws/aws-sdk-go/service/route53/route53iface"
 )
 
 func TestSetupRoute53(t *testing.T) {
-	f = func(credential *credentials.Credentials, endpoint *string) route53iface.Route53API {
+	f = func(opts session.Options) route53iface.Route53API {
 		return fakeRoute53{}
 	}