[Engineering] Proposal regarding the future of X-Wikimedia-Debug and testwiki

[Alex Monk]

Forwarding to wikitech-l since this is not really specific to staff, but
all shell users.

On 25 January 2016 at 20:39, Ori Livneh <ori at wikimedia.org> wrote:

> The X-Wikimedia-Debug header, for those of you who don't know, is an HTTP
> request header that you can set on your requests (either manually, or by
> using the Chrome[1] or Firefox[2] extensions). Requests bearing this header
> are always treated as cache misses by Varnish, and they are always routed
> to the same backend, mw1017.
>
> In addition to handling X-Wikimedia-Debug requests, mw1017 is also
> configured as the sole application server backend for all requests to
> test.wikimedia.org. This was set up before X-Wikimedia-Debug existed, and
> as a debugging tool it is (IMO) inferior to it, because X-Wikimedia-Debug
> allows you to test code changes against any production wiki.
>
> What I've seen happen before is developers (like me -- I've done this
> before) live-hack code on mw1017 to debug some issue that is only showing
> up in production. This can cause testwiki to break, which annoys developers
> and editors who use testwiki for testing things like Lua modules or editing
> functionality on mobile apps.
>
> To reduce contention for mw1017, I propose that we do the following:
>
> 1) Keep testwiki, but don't special-case it in Varnish
> (in other words, have testwiki requests go to the standard app server pool)
>
> 2) Reserve mw1017 exclusively for X-Wikimedia-Debug requests
>
> 3) Add a service alias (appservers-debug.svc.eqiad.wmnet) for mw1017 and
> update the varnish backend config to use that, rather than hard-code mw1017
> in VCL.
>
> Thoughts?
>
>  [1]:
> https://chrome.google.com/webstore/detail/wikimediadebug/binmakecefompkjggiklgjenddjoifbb?hl=en-US
>  [2]:
> https://addons.mozilla.org/en-US/firefox/addon/wikimedia-debug-header/
>
>
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>
>
-- 
Alex Monk
VisualEditor/Editing team
https://wikimediafoundation.org/wiki/User:Krenair_(WMF)
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