http 500, "timeout / couch_config, get httpd x-forwarded-host"

Binary package hint: couchdb

it caused HTTP 500 and couchdb described it as
{"error":"timeout","reason":"{gen_server,call,\n [couch_config,\n {get,\"httpd\",\"x_forwarded_host\",\"X-Forwarded-Host\"}]}"}
{gen_server,call,2},
             {couch_httpd,absolute_uri,2},
             {couch_httpd_db,db_doc_req,3},
             {couch_httpd_db,do_db_req,2},
             {couch_httpd,handle_request,5},
             {mochiweb_http,headers,5},
             {proc_lib,init_p_do_apply,3}