Hi Itay Malka,
If you have an existing OpenLDAP server, you can use `Cache Refresh` service to pull users data from your backend server. **Cache Refresh** pulls user data and store them on gluu server local database. You will find more details on the documentation: https://gluu.org/docs/gluu-server/4.3/user-management/ldap-sync/
Regards ~ Shakil