Implementation details of RegionFromEndpointGuesser

Author: DaveCTurner

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

@@ -26,6 +26,12 @@
  * Simple mapping from S3 endpoint hostnames to AWS region names, in case the user does not specify a region.
  */
 class RegionFromEndpointGuesser {
+    /*
+     * Loads JAR resource "regions_by_endpoint.txt" into a map from S3 endpoint hostnames to AWS region names, in case the user specifies a
+     * regional endpoint but not a region. This allows Elasticsearch to guess an appropriate AWS region name, and keep working, if a user
+     * does not specify one. This is a best-effort attempt for backwards compatibility: AWS SDK V1 would extrapolate the correct region but
+     * V2 considers it a fatal error not to be told the region name explicitly.
+     */
 
     private static final Map<String, String> regionsByEndpoint;