prefer GetBucketLocation() API for s3-compatible endpoints (#1112)

* use get-bucket-location api for non-aws-s3 endpoints

* Update pkg/objectstore/bucket.go

Co-authored-by: Tom Manville <tom@kasten.io>

Co-authored-by: Shikhar Mall <shikhar@kasten.io>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
Co-authored-by: Tom Manville <tom@kasten.io>

pkg/objectstore/bucket.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"path"
 
+	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/aws/request"
 	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/aws/aws-sdk-go/service/s3"
@@ -193,6 +194,27 @@ func s3BucketRegion(ctx context.Context, cfg ProviderConfig, sec Secret, bucketN
 		return "", errors.Wrapf(err, "failed to create session, region = %s", r)
 	}
 	svc := s3.New(s)
+
+	// s3-compatible stores may not support s3manager.GetBucketRegion() API, so
+	// prefer to use the get-bucket-location API instead
+	if cfg.Endpoint != "" {
+		resp, err := svc.GetBucketLocation(&s3.GetBucketLocationInput{
+			Bucket: aws.String(bucketName),
+		})
+		if err == nil {
+			if resp.LocationConstraint == nil { // per the AWS SDK doc a nil location means us-east-1
+				return "us-east-1", nil
+			}
+			return *resp.LocationConstraint, nil
+		}
+		log.Error().
+			WithContext(ctx).
+			WithError(err).
+			Print("GetBucketLocation() failed, falling back to GetBucketRegion()", field.M{"config": c})
+		// fallback to GetBucketRegion() API if we fail (could be due to
+		// access-denied or incorrect policies etc)
+	}
+
 	return s3manager.GetBucketRegionWithClient(ctx, svc, bucketName, func(r *request.Request) {
 		// GetBucketRegionWithClient() uses credentials.AnonymousCredentials by
 		// default which fails the api request in AWS China. We override the