HTTPS using TLS can be required in OpenSearch (formerly named ElastiSearch) for node-to-node encryption while data is in transit. Encryption is considered best practice and can help protect sensitive data. For more information, see the AWS Documentation.
References:
https://docs.aws.amazon.com/opensearch-service/latest/developerguide/ntn.html
In AWS Console -
In Terraform -
References:
https://docs.aws.amazon.com/opensearch-service/latest/developerguide/security.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/elasticsearch_domain#enforce_https