How to view Elasticserarch AWS cluster settings
Yes, it is an AWS constraint on ElasticSearch prior to version 5.3.
Prior to Elasticsearch 5.3, the _cluster/settings API on Amazon ES domains supported only the HTTP PUT method, not the GET method.
AWS supports _cluster/settings after Elasticsearch 5.3, and other Elasticsearch operations, but not all. You can refer to their doc:https://docs.aws.amazon.com/elasticsearch-service/latest/developerguide/aes-supported-es-operations.html#es_version_api_notes