Update comment re HTTP retry
@@ -92,7 +92,9 @@ func join(joinAddr string, advAddr string, tlsConfig *tls.Config, logger *log.Lo
continue
case http.StatusBadRequest:
// One possible cause is that the target server is listening for HTTPS, but a HTTP
- // attempt was made. Switch the protocol to HTTPS, and try again. This
+ // attempt was made. Switch the protocol to HTTPS, and try again. This can happen
+ // when using the Disco service, since it doesn't record information about which
+ // protocol a registered node is actually using.
if isHTTPS, err := httpd.CheckHTTPS(fullAddr); err != nil {
return "", err
} else if isHTTPS {
