Reverse proxy_

Hi,

I am setting up a reverse-proxy system with Nginx (0.8.32) both as
back-end and proxy. The system is used for delivering static large
files.

What I would like to achieve is caching the files on the proxies as long
as possible offloading the back-end. I would also like the proxy to
react to changes on the back-end, but without retransmitting already
cached unmodified content.

My problem is that I’m not able to get the proxy to revalidate
unmodified static content without retransmitting the already cached
file. E.g. if I set proxy_cache_valid for 200/OK delivered content to 60
minutes the proxy won’t react to changes in the back-end for that period
of time, and if I set it to 1 minute the file will be retransmitted from
back-end to proxy every minute, if requested from the proxy by a client.
What I would like is, for example, for the proxy to revalidate cached
content with I-M-S set to the time of the content being cached and if
not modified refreshing the validity of the previously cached content
and returning it to the client.

I’ve looked through the documentation and played with cache-control
directives like for example pre/post-check without succeeding in
creating this behaviour. There probably is an obvious answer to this
question, only I haven’t been able to find it.

Kind regards,
Fredrik Widlund

Hello!

On Tue, Feb 16, 2010 at 04:25:21PM +0100, Fredrik Widlund wrote:

retransmitting already cached unmodified content.
and if not modified refreshing the validity of the previously
cached content and returning it to the client.

I’ve looked through the documentation and played with
cache-control directives like for example pre/post-check without
succeeding in creating this behaviour. There probably is an
obvious answer to this question, only I haven’t been able to
find it.

It’s not currently supported.

Maxim D.

Hi Maxim,

Thanks for the answer! Are there currently any plans to add support for
this in the near future?

Kind regards,
Fredrik Widlund

-----Ursprungligt meddelande-----
Från: Maxim D. [mailto:[email protected]]
Skickat: den 16 februari 2010 16:58
Till: [email protected]
Ämne: Re: reverse proxy_

Hello!

On Tue, Feb 16, 2010 at 04:25:21PM +0100, Fredrik Widlund wrote:

retransmitting already cached unmodified content.
and if not modified refreshing the validity of the previously
cached content and returning it to the client.

I’ve looked through the documentation and played with
cache-control directives like for example pre/post-check without
succeeding in creating this behaviour. There probably is an
obvious answer to this question, only I haven’t been able to
find it.

It’s not currently supported.

Maxim D.


nginx mailing list
[email protected]
http://nginx.org/mailman/listinfo/nginx

Hi,

Explicitly purging the cache would not work in this scenario though.

Why is this not doable? I’m even considering adding support for this
myself into Nginx, since we really need it and also since it seemed kind
of natural?

This could of course be an optional feature, but it would be interesting
to know what this breaks?

Regards,
Fredrik

On Wed, Feb 24, 2010 at 3:20 AM, Fredrik Widlund
[email protected] wrote:

Why is this not doable? I’m even considering adding support for this myself into Nginx, since we really need it and also since it seemed kind of natural?

This could of course be an optional feature, but it would be interesting to know what this breaks?

I agree… this shouldn’t be impossible by any stretch. Squid seems to
handle this scenrio just fine, and the Cache-Control infrastructure of
HTTP/1.1 was designed explicitly to enable this behavior.

What is the scnario that doesn’t work for this?

RPM

On Tue, Feb 16, 2010 at 8:07 AM, Fredrik Widlund
[email protected] wrote:

Hi Maxim,

Thanks for the answer! Are there currently any plans to add support for this in the near future?

Kind regards,
Fredrik Widlund

It’s not really doable as far as I understand things, at least not in
a general, portable way that satisfies all backends.

What you CAN do is you use ngx_cache_purge to have the backend inform
nginx when content has changed. This is the only method that is
general enough for any backend, but it of course requires you to do
something.

http://labs.frickle.com/nginx_cache_purge

Good luck.

– Merlin

Hi Merlin,

Could you elaborate a bit around the problems with achieving this in a
general way? It would be valuable to know before one tries to solve the
problem as good as is possible.

Kind regards,
Fredrik Widlund

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