Change 535860 had a related patch set uploaded (by Gilles; owner: Gilles):
[operations/puppet@production] Gzip SVGs served by MediaWiki

https://gerrit.wikimedia.org/r/535860

Nice catch. I could've sworn this was done already, but maybe it got lost somehow. Perhaps in the transition from bits to canonical domain, or when we introduced the static.php router.

For JS files, it does still apply gzip compression, e.g. https://en.wikipedia.org/w/skins/Vector/vector.js.

See also:

• T63443: Enable gzip transfer encoding for png and ico files in /static
• T99096: Make Varnish cache for /static/$wmfbranch/ expire when resources change within branch lifetime

# Multiversion static files (T99096)
RewriteRule ^/w/skins/.*$ /w/static.php [PT]
RewriteRule ^/w/resources/.*$ /w/static.php [PT]
RewriteRule ^/w/extensions/.*$ /w/static.php [PT]

Reporting a discussion happened on IRC: the change looks good, but it seems that Varnish/ATS explicitly unsed the Accept-Encoding request header before calling mediawiki:

https://gerrit.wikimedia.org/r/#/q/I2e7576fa9b5e2fd6f154f1be0e51cec96aa966ca (ATS)
https://gerrit.wikimedia.org/r/#/c/operations/puppet/+/421267 (Varnish)

As far as I can understand if you want a change in external behavior you'll need to do a ATS/VCL config change (so ATS/Varnish will gzip specific contents before sending to the client). There is a do_gzip VCL setting that might be useful to check:

https://github.com/wikimedia/puppet/blob/da1b4c7429b861121392a63c20f96d434daea20d/modules/varnish/templates/vcl/wikimedia-common.inc.vcl.erb#L451-L454

Change 537974 had a related patch set uploaded (by Gilles; owner: Gilles):
[operations/puppet@production] Lower gzip threshold for SVGs served by MediaWiki

https://gerrit.wikimedia.org/r/537974

TODO: add comment in the Apache config code pointing to the VCL and explaining the context

Change 537974 merged by Vgutierrez:
[operations/puppet@production] Lower gzip threshold for SVGs served by MediaWiki

https://gerrit.wikimedia.org/r/537974

Change 535860 abandoned by Gilles:
Gzip SVGs served by MediaWiki

https://gerrit.wikimedia.org/r/535860

Change 539842 had a related patch set uploaded (by Gilles; owner: Gilles):
[operations/puppet@production] Document Apache gzip sidestepping

https://gerrit.wikimedia.org/r/539842

hey @Gilles

We encountered an incident related to this change.
Described in comment T234183#5533440. I suspect either there's something to fix here still, or that there's just a wrong cached version of the svgs in varnish.

Indeed, it seems like Varnish claims that the content is gzipped but it actually isn't.

I think this is a Varnish bug or limitation, because if I manually cachebust the URL, the response is correctly gzipped: https://test.m.wikidata.org/w/extensions/Wikibase/view/lib/wikibase-termbox/assets/pen.svg?thisisnew

It seems like this object was cached uncompressed before the change, and that Varnish serves it as-is now, with the compressed headers, because in the new logic these objects are compressed.

Varnish should check that when do_gzip is enabled, the object already stored is indeed gzipped, but it doesn't. Or, if it decides to serve the uncompressed copy it already has, it shouldn't apply the gzip headers.

@Vgutierrez is there a simple way to purge all responses with content-type image/svg+xml from the Varnish text cluster? Is it worth reporting an upstream bug to Varnish?

@Gilles, yeah, with varnishadm ban like it's documented on https://wikitech.wikimedia.org/wiki/Varnish#One-off_purges_(bans) but I think that we should purge the responses with content-type image/svg+xml and content-length < 860, cause for bigger images do_gzip was already enabled.

Yep, exactly. In fact you can go as far as only banning content-length between 150 and 860 (inclusive).

@Vgutierrez purged SVGs whose content-length is > 100 and <= 899 in both cache layers for text and upload.

Actually I'm missing the backend layer on the upload cluster.. it's powered by ATS and the procedure is different

Change 542996 had a related patch set uploaded (by Ema; owner: Ema):
[operations/puppet@production] ATS: lower compress plugin minimum-content-length

https://gerrit.wikimedia.org/r/542996

Change 542996 abandoned by Ema:
ATS: lower compress plugin minimum-content-length

Reason:
Plugin disabled altogether for now. It's unusable as it is, see https://gerrit.wikimedia.org/r/#/c/operations/puppet/ /559053/

https://gerrit.wikimedia.org/r/542996

Change 539842 merged by Filippo Giunchedi:
[operations/puppet@production] Document Apache gzip sidestepping

https://gerrit.wikimedia.org/r/539842