Thank you both for your comments.

We attempted to set the Last-Modified header because expires and cache-control alone did not seem to work at all, the object is still transferred over the wire. We even increased the expires time from two to six hours but different browsers still download the object. These are the object's response headers:

Cache-Control:public,max-age=28800
Connection:keep-alive
Content-Encoding:gzip
Content-Type:application/x-javascript; charset=utf-8
Date:Wed, 04 Jul 2012 13:45:37 GMT
Expires:Wed, 04 Jul 2012 21:45:37 GMT
Transfer-Encoding:chunked

I don't see anything really missing. Any hints to share?

Thanks!


-----Original message-----
> From:Brian Akins <brian@akins.org>
> Sent: Wed 04-Jul-2012 15:11
> To: nginx@nginx.org
> Subject: Re: SSI and expires header
>
> On Jul 4, 2012, at 5:56 AM, James Lee wrote:
>
>    location /ssi/ {
>        ssi on;
>        expires 1w;
>        add_header Last-Modified 'not added';
>    }
>    location /ssi-with-last-modified/ {
>        proxy_pass        http://localhost/ssi/ http://localhost/ssi/ ;
>        proxy_set_header  Host www.HOST.co.uk http://www.HOST.co.uk ;
>        add_header Last-Modified 'this works!';
>    }
>
>
> With this config, every request will actually cause two hits to nginx. 
>
> Last-Modified is removed from SSI in every web server I know because you'd really need to show the last modified time of the newest included element. Also, if there are dynamic elements, how do you handle those?
>
> I did  simple Lua header filter that adds the current time to Last-Modified when needed.  Depending on which browsers you need to support, however, just adding Expires and/or Cache-Control headers is enough to get the browser to cache. I know that not all browsers behave correctly, however.
>
> Something simple like:
>
> header_filter_by_lua '
>      ngx.header["Last-Modified"] = ngx.http_time(ngx.time())
> ';
>
> Of course, you may want to check to see if it's already been set, only set if a flag is present, etc.
>
>
> The "proxy to yourself" solution is unacceptable for a busy site.
>
> --Brian
>
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>

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