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

[Alex Monk]

Trying again from a different address

On 26 January 2016 at 01:04, Alex Monk <amonk at wikimedia.org> wrote:

> 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/
>>
>>
>> _______________________________________________
>> Engineering mailing list
>> Engineering at lists.wikimedia.org
>> https://lists.wikimedia.org/mailman/listinfo/engineering
>>
>>
> --
> Alex Monk
> VisualEditor/Editing team
> https://wikimediafoundation.org/wiki/User:Krenair_(WMF)
>
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