Thank you. Yes, it acts like frontend proxy before forwarding any request into the backend (strfry internal relay). However, RELAYS_SOURCE determines where to fetch/aggregate Nostr events (kind 1) before classifying them into various category and send them into target relay (strfry internal relay). UPSTREAM_WS_URL is the correct one for settings which relay to be the target of proxy. I have run several tools in this docker image, maybe it makes a bit confusing 😅