When running embedded in API Gateway, the external Elasticsearch instances have to be clustered by modifying the <Elastic_Dir>/config/elasticsearch.yml file within each API Gateway instance. You must provide the cluster configurations in the elasticsearch.yml file in the Install_Dir/config/ folder before starting the external Elasticsearch for the very first time. When you start external Elasticsearch, the node auto-bootstraps itself into a new cluster. You cannot change the configuration after bootstrap and thus, external Elasticsearch does not merge separate clusters together after they have formed, even if you subsequently try and configure all the nodes into a single cluster. For more information, see https://www.elastic.co/guide/en/elasticsearch/reference/8.2/index.html.