Merge branch 'update-realtime-docs' into 'master'

Updates realtime documentation for the Frontend

See merge request !10038

doc/development/frontend.md

@@ -38,14 +38,21 @@ When writing code for realtime features we have to keep a couple of things in mi
 1. Do not overload the server with requests.
 1. It should feel realtime.
 
-Thus, we must strike a balance between sending requests and the feeling of realtime. Use the following rules when creating realtime solutions.
-
-1. The server will tell you how much to poll by sending `X-Poll-Interval` in the header. Use that as your polling interval. This way it is easy for system administrators to change the polling rate. A `X-Poll-Interval: -1` means you should disable polling, and this must be implemented. 
-1. A response of `HTTP 429 Too Many Requests`, should disable polling as well. This must also be implemented.
+Thus, we must strike a balance between sending requests and the feeling of realtime.
+Use the following rules when creating realtime solutions.
+
+1. The server will tell you how much to poll by sending `Poll-Interval` in the header.
+Use that as your polling interval. This way it is easy for system administrators to change the
+polling rate.
+A `Poll-Interval: -1` means you should disable polling, and this must be implemented.
+1. A response with HTTP status `4XX` or `5XX` should disable polling as well.
 1. Use a common library for polling.
-1. Poll on active tabs only. Use a common library to find out which tab currently has eyes on it. Please use [Focus](https://gitlab.com/andrewn/focus). Specifically [Eyeballs Detector](https://gitlab.com/andrewn/focus/blob/master/lib/eyeballs-detector.js).
-1. Use regular polling intervals, do not use backoff polling, or jitter, as the interval will be controlled by the server.
-1. The backend code will most likely be using etags. You do not and should not check for status `304 Not Modified`. The browser will transform it for you.
+1. Poll on active tabs only. Use a common library to find out which tab currently has eyes on it.
+Please use [Focus](https://gitlab.com/andrewn/focus). Specifically [Eyeballs Detector](https://gitlab.com/andrewn/focus/blob/master/lib/eyeballs-detector.js).
+1. Use regular polling intervals, do not use backoff polling, or jitter, as the interval will be
+controlled by the server.
+1. The backend code will most likely be using etags. You do not and should not check for status
+`304 Not Modified`. The browser will transform it for you.
 
 ### Vue