The CR Service is under a permissive license.
HAPI FHIR Server
HAPI is licensed under the Apache 2.0 license. See: https://hapifhir.io/hapi-fhir/license.html.
ElasticSearch is Apache 2.0 and primarily supported by Elastic.co who offer open and open plus proprietary releases and a stack of apps based on ElasticSearch (like the Kibana dashboarding platform).
This CR implementation only uses core, open features, not enterprise features. Netflix and Amazon Web Services also have a distribution of ElasticSearch that is 100% open source and that they have added open source enterprise features to like authentication. Developers who want to test other distributions and features of ElasticSearch are welcome to do so and encouraged to share their experiences with the maintainers.