Update modules/repository-s3/src/main/java/org/elasticsearch/repositories/s3/S3Service.java

Co-authored-by: Dianna Hohensee <[email protected]>

Author: nicktindall

modules/repository-s3/src/main/java/org/elasticsearch/repositories/s3/S3Service.java

@@ -256,7 +256,8 @@ protected S3ClientBuilder buildClientBuilder(S3ClientSettings clientSettings, Sd
         if (Strings.hasLength(clientSettings.endpoint)) {
             String endpoint = clientSettings.endpoint;
             if ((endpoint.startsWith("http://") || endpoint.startsWith("https://")) == false) {
-                // Default protocol to https if not specified
+                // The SDK does not know how to interpret endpoints without a scheme prefix and will error. Therefore, when the scheme is
+                // absent, we'll supply HTTPS as a default to avoid errors.
                 // See https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/client-configuration.html#client-config-other-diffs
                 endpoint = "https://" + endpoint;
                 LOGGER.info("Defaulting to https for endpoint with no scheme [{}]", clientSettings.endpoint);