Simple question about proxy cache

[John Moore]

On 17/03/13 23:08, Maxim Dounin wrote:
> Hello!
>
> On Sun, Mar 17, 2013 at 08:08:39PM +0000, John Moore wrote:
>
>> 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?
> 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).
>

Excellent - thanks, Maxim! That's got me sorted now, it all seems to be 
working as planned.