I tried having sourcegraph1.wmflabs.org be a proxy to codesearch-sourcegraph1.eqiad.wmflabs:7080 but horizon gave me HTTP 500:
Error: Unable to create proxy: <!DOCTYPE HTML PUBLIC "-W3CDTD HTML 3.2 Final//EN"> <title>500 Internal Server Error</title> <h1>Internal Server Error</h1> <p>The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.</p>