Rewrite Vary header before stored in proxy_cache
mdounin at mdounin.ru
Mon Oct 24 12:49:23 UTC 2016
On Mon, Oct 24, 2016 at 06:38:25AM +0200, Lucas Rolff wrote:
> Hi guys,
> I'm building a small nginx reverse proxy to take care of a bunch of static
> files for my clients - and it works great.
> One thing I'm facing though is that some client sites sent "Vary:
> Accept-Encoding, User-Agent" - which gives an awful cache hit rate - since
> proxy_cache takes this into account, unless I use something like
> "proxy_ignore_headers Vary;"
> But ignoring Vary headers can cause other issues such as gzipped content
> being sent to a non-gzip client.
> So I'm looking for a way to basically rewrite the vary header to "Vary:
> Accept-Encoding" before storing it in proxy_cache - but I wonder if this is
> even possible in nginx, and if yes - can you give any pointers?
> I found a temporary fix, and that is to ignore the Vary header, and using a
> custom variable as a part of the cache key, that is either "", "gzip" or
> "deflate" (I use a map to look at the Accept-Encoding header from the
> This works great - but I rather keep the cache key a bit clean (since I'll
> use it later)
> Do you guys have any recommendations how to make this happen?
The best possible solution I can think of is to ask the client to fix
the Vary header it returns. Using User-Agent in Vary is something
one shouldn't use without a very good reason, and if there a
reason - it's likely a bad idea to strip from the Vary header.
And if there are no reasons, then it shouldn't be returned in the
> Also as a side note, if I remove the custom variable from the cache key,
> how would one actually purge the file then? I assume I have to send
> different purge requests, since the cached file is based on the Vary:
> accept-encoding - so I'd have to purge at least the amount of cached
> encodings right?
When using purge as availalbe in nginx-plus
(http://nginx.org/r/proxy_cache_purge), it takes care of removing
all cached variants, much like it does for wildcard purge requests.
> Also I could opt for another way, and that's always requesting a
> uncompressed file from the origin (Is it simply not sending the
> accept-encoding header, or should I do something else?), and then on every
> request either decide to gzip it or not - the downside I see here, is the
> fact that most clients request gzip,deflate content, so having to compress
> on every request will use additional CPU resources.
This can be done easily, just
proxy_set_header Accept-Encoding "";
should be enough. Alternatively, you can use
proxy_set_header Accept-Encoding gzip;
to always ask gzipped resources and gunzip them when needed, see
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