Use current region to find bucket region

Author: keithduncan

s3secrets-helper/main.go

@@ -16,9 +16,6 @@ const (
 	envPipeline   = "BUILDKITE_PIPELINE_SLUG"
 	envRepo       = "BUILDKITE_REPO"
 	envCredHelper = "BUILDKITE_PLUGIN_S3_SECRETS_CREDHELPER"
-
-	envDefaultRegion = "AWS_DEFAULT_REGION"
-	defaultRegion    = "us-east-1"
 )
 
 func main() {
@@ -42,11 +39,7 @@ func mainWithError(log *log.Logger) error {
 		return fmt.Errorf("%s or %s required", envPrefix, envPipeline)
 	}
 
-	region := os.Getenv(envDefaultRegion)
-	if region == "" {
-		region = defaultRegion
-	}
-	client, err := s3.New(region)
+	client, err := s3.New(bucket)
 	if err != nil {
 		return err
 	}

s3secrets-helper/s3/s3.go

@@ -2,37 +2,70 @@ package s3
 
 import (
 	"io/ioutil"
+	"os"
 
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/aws/awserr"
+	"github.com/aws/aws-sdk-go/aws/ec2metadata"
 	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/aws/aws-sdk-go/service/s3"
+	"github.com/aws/aws-sdk-go/service/s3/s3manager"
 	"github.com/buildkite/elastic-ci-stack-s3-secrets-hooks/s3secrets-helper/v2/sentinel"
 )
 
+const envDefaultRegion = "AWS_DEFAULT_REGION"
+
 type Client struct {
 	s3 *s3.S3
+	bucket string
 }
 
-func New(region string) (*Client, error) {
-	sess, err := session.NewSession(&aws.Config{
-		Region: &region,
+func New(bucket string) (*Client, error) {
+	sess, err := session.NewSession()
+	if err != nil {
+		return nil, err
+	}
+
+	currentRegion := os.Getenv(envDefaultRegion)
+	// Discover our executing region using the IMDS
+	if currentRegion == "" {
+		idms := ec2metadata.New(sess)
+		currentRegion, _ = idms.Region()
+	}
+	// Fall back to us-east-1 :(
+	if currentRegion == "" {
+		currentRegion = "us-east-1"
+	}
+
+	// Using the current region (or a guess) find where the bucket lives
+	bucketRegion, err := s3manager.GetBucketRegion(aws.BackgroundContext(), sess, bucket, currentRegion)
+	if err != nil {
+		return nil, err
+	}
+
+	sess, err = session.NewSession(&aws.Config{
+		Region: &bucketRegion,
 	})
 	if err != nil {
 		return nil, err
 	}
 	return &Client{
 		s3: s3.New(sess),
+		bucket: bucket,
 	}, nil
 }
 
+func (c *Client) Bucket() (string) {
+	return c.bucket
+}
+
 // Get downloads an object from S3.
 // Intended for small files; object is fully read into memory.
 // sentinel.ErrNotFound and sentinel.ErrForbidden are returned for those cases.
 // Other errors are returned verbatim.
-func (c *Client) Get(bucket, key string) ([]byte, error) {
+func (c *Client) Get(key string) ([]byte, error) {
 	out, err := c.s3.GetObject(&s3.GetObjectInput{
-		Bucket: &bucket,
+		Bucket: &c.bucket,
 		Key:    &key,
 	})
 	if err != nil {
@@ -59,8 +92,8 @@ func (c *Client) Get(bucket, key string) ([]byte, error) {
 // 200 OK returns true without error.
 // 404 Not Found and 403 Forbidden return false without error.
 // Other errors result in false with an error.
-func (c *Client) BucketExists(bucket string) (bool, error) {
-	if _, err := c.s3.HeadBucket(&s3.HeadBucketInput{Bucket: &bucket}); err != nil {
+func (c *Client) BucketExists() (bool, error) {
+	if _, err := c.s3.HeadBucket(&s3.HeadBucketInput{Bucket: &c.bucket}); err != nil {
 		if aerr, ok := err.(awserr.Error); ok {
 			switch aerr.Code() {
 			// https://github.com/aws/aws-sdk-go/issues/2593#issuecomment-491436818

s3secrets-helper/secrets/secrets.go

@@ -12,8 +12,9 @@ import (
 
 // Client represents interaction with AWS S3
 type Client interface {
-	Get(bucket, key string) ([]byte, error)
-	BucketExists(bucket string) (bool, error)
+	Bucket() (string)
+	Get(key string) ([]byte, error)
+	BucketExists() (bool, error)
 }
 
 // Agent represents interaction with an ssh-agent process
@@ -56,12 +57,12 @@ type Config struct {
 // functionality; secrets are downloaded from S3, and loaded into ssh-agent
 // etc.
 func Run(conf Config) error {
-	bucket := conf.Bucket
+	bucket := conf.Client.Bucket()
 	log := conf.Logger
 
 	log.Printf("~~~ Downloading secrets from :s3: %s", bucket)
 
-	if ok, err := conf.Client.BucketExists(bucket); !ok {
+	if ok, err := conf.Client.BucketExists(); !ok {
 		if err != nil {
 			log.Printf("+++ :warning: Bucket %q not found: %v", bucket, err)
 		} else {
@@ -102,7 +103,7 @@ func getSSHKeys(conf Config, results chan<- getResult) {
 	for _, k := range keys {
 		conf.Logger.Printf("- %s", k)
 	}
-	go GetAll(conf.Client, conf.Bucket, keys, results)
+	go GetAll(conf.Client, conf.Client.Bucket(), keys, results)
 }
 
 func getEnvs(conf Config, results chan<- getResult) {
@@ -116,7 +117,7 @@ func getEnvs(conf Config, results chan<- getResult) {
 	for _, k := range keys {
 		conf.Logger.Printf("- %s", k)
 	}
-	go GetAll(conf.Client, conf.Bucket, keys, results)
+	go GetAll(conf.Client, conf.Client.Bucket(), keys, results)
 }
 
 func getGitCredentials(conf Config, results chan<- getResult) {
@@ -128,7 +129,7 @@ func getGitCredentials(conf Config, results chan<- getResult) {
 	for _, k := range keys {
 		conf.Logger.Printf("- %s", k)
 	}
-	go GetAll(conf.Client, conf.Bucket, keys, results)
+	go GetAll(conf.Client, conf.Client.Bucket(), keys, results)
 }
 
 func handleSSHKeys(conf Config, results <-chan getResult) error {
@@ -241,7 +242,7 @@ func GetAll(c Client, bucket string, keys []string, results chan<- getResult) {
 		// goroutine immediately fetches from S3, then waits for its turn to send
 		// to the results channel; concurrent fetch, ordered results.
 		go func(k string, link <-chan chan<- getResult, nextLink chan<- chan<- getResult) {
-			data, err := c.Get(bucket, k)
+			data, err := c.Get(k)
 			results := <-link // wait for results channel from previous goroutine
 			results <- getResult{bucket: bucket, key: k, data: data, err: err}
 			nextLink <- results // send results channel to the next goroutine