Elasticsearch licence policy and fess with other search engines

(from github.com/jobaudev)
Elasticsearch 7.4 has a hybrid license model which mixes free modules under Apache 2.0 License with the proprietary Elastic License. So if we use Fess, we need Elastic License. Is this correct?

Q 1: Can we replace the Elasticsearch for Fess with Solr?
Q 2: Can we replace the Elasticsearch for Fess with Amazons free version of Elasticsearch ‘Open Distro’ (https://github.com/orgs/opendistro-for-elasticsearch/people)?
Q 3: Is there an other Open Source alternative?

Thx a lot

(from github.com/marevol)

Q 1: Can we replace the Elasticsearch for Fess with Solr?

No.

Q 2: Can we replace the Elasticsearch for Fess with Amazons free version of Elasticsearch ‘Open Distro’ (https://github.com/orgs/opendistro-for-elasticsearch/people)?

We do not test Fess on it… but I think it works.

Q 3: Is there an other Open Source alternative?

See https://www.elastic.co/downloads/elasticsearch-oss
It includes only OSS features.

(from github.com/jobaudev)
Thank you very much for the super fast response. I’m excited!