Warning
The Google Search Appliance (GSA) compatible API (/gsa/) was removed in Fess 14.8. Neither Fess 15.9 itself nor the plugins that serve the legacy APIs (fess-webapp-classic-api and fess-webapp-v1-api) implement /gsa/, so setting web.api.gsa has no effect and a request to /gsa/ returns 404. To search, use /api/v2/search described in Search API.