Simple question about proxy cache

I’ve used nginx as a reverse proxy server for a long while but I’ve not
tried out the proxy cache until today, and I have to say I’m a little
bit confused by what I’m seeing in the cache log, and I’m wondering
whether I’ve set things up correctly. My requirements are actually
pretty simple. I have a couple of locations which I want to proxy to
another server and cache the results. Thus:

       location /media/house_images/{
         proxy_pass http://backend;
         proxy_cache one;
      }

      location /media/boat_images/{
         proxy_pass http://backend;
         proxy_cache one;
      }

Apart from this, I don’t want any cacheing of responses to be done. I am
assuming that the default is NOT to cache unless a cache zone is
specified (at the server or location level, presumably), so either
omitting a proxy_cache or specifying ‘proxy_cache off’ should be
sufficient to achieve this, should it not?

Two things are puzzling me, though. Firstly, in the cache log, I’m
seeing the URLs of all kinds of requests which SHOULD NOT be cached, and
I’m wondering whether all requests are logged whether they’re cached or
not - I certainly hope this is the case and it’s not actually cacheing
these responses. I would definitely prefer to only see entries in the
log for requests matching locations for which a cache has been
specified. I presume this is possible?

Secondly, the very requests which I would expect to be cached are all
showing up in the log with the word ‘MISS’ in the $upstream_cache_status
column.

So, I am worried that I’m currently cacheing everything EXCEPT the pages
I actually want to be cached!

Could someone please clarify whether my assumptions are correct, and
maybe explain how I should set up cacheing to do just what I want, in
the simplest way? Thanks.

John

Hello!

On Sun, Mar 17, 2013 at 08:08:39PM +0000, John M. wrote:

      }

omitting a proxy_cache or specifying ‘proxy_cache off’ should be
sufficient to achieve this, should it not?

Yes, without proxy_cache (or with “proxy_cache off”) configured in
a location cache won’t be used.

Two things are puzzling me, though. Firstly, in the cache log, I’m
seeing the URLs of all kinds of requests which SHOULD NOT be cached, and
I’m wondering whether all requests are logged whether they’re cached or
not - I certainly hope this is the case and it’s not actually cacheing
these responses. I would definitely prefer to only see entries in the
log for requests matching locations for which a cache has been
specified. I presume this is possible?

You can configure logs for a specific location, see
http://nginx.org/r/access_log.

Secondly, the very requests which I would expect to be cached are all
showing up in the log with the word ‘MISS’ in the $upstream_cache_status
column.

This usually happens if your backend doesn’t specify allowed cache
time (in this case, proxy_cache_valid should be used to set one,
see http://nginx.org/r/proxy_cache_valid) or if backend responses
doesn’t allow cache to be used (either directly with
Cache-Control/Expires headers, or indirectly with Set-Cookie
header, see http://nginx.org/r/proxy_ignore_headers).


Maxim D.
http://nginx.org/en/donation.html

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