Forum: NGINX SSI and expires header

Hello,

We use SSI for serving a specific file but we want it to be cached by 
the clients for a few hours. We know SSI removes the Expires header set 
by the standard headers module so we wrote a small perl_set sub that 
returns a proper HTTP expires date in the future which we set using the 
headers_more module. Testing via curl -i returns and checking in the 
browser confirms the Expires header is set correctly. We also output a 
Cache-Control header.

The browser, however, doesn't seem to cache the object so we must do 
something wrong here. I assume we also need a LastModified header but 
how can we force to send that header while SSI is on?

Thanks,
Markus

We also tried using the Nginx sub module but this module as well strips 
away any Last-Modified header, even when we force the Last-Modified 
header with headers more using a perl_set subroutine returning the 
proper date.

Any suggestions are very welcome :)
Markus



-----Original message-----

On 25/06/12, 15:12:58, "Markus Jelsma" <markus.jelsma@openindex.io> 
wrote
regarding SSI and expires header:

Hello,

> We use SSI for serving a specific file but we want it to be cached
> by the clients for a few hours. We know SSI removes the Expires
> header set by the standard headers module so

SSI + expires works for me, example below.


> The browser, however, doesn't seem to cache the object so we must do
> something wrong here. I assume we also need a LastModified header
> but how can we force to send that header while SSI is on?


    location /ssi/ {
        ssi on;
        expires 1w;
        add_header Last-Modified 'not added';
    }
    location /ssi-with-last-modified/ {
        proxy_pass        http://localhost/ssi/;
        proxy_set_header  Host www.HOST.co.uk;
        add_header Last-Modified 'this works!';
    }



$ curl -I http://www.HOST.co.uk/ssi/
HTTP/1.1 200 OK
Server: nginx/1.2.2
Date: Wed, 04 Jul 2012 09:44:28 GMT
Content-Type: text/html; charset=8858-1
Connection: keep-alive
Vary: Accept-Encoding
Expires: Wed, 11 Jul 2012 09:44:28 GMT
Cache-Control: max-age=604800

$ curl -I http://www.HOST.co.uk/ssi-with-last-modified/
HTTP/1.1 200 OK
Server: nginx/1.2.2
Date: Wed, 04 Jul 2012 09:44:38 GMT
Content-Type: text/html; charset=8858-1
Connection: keep-alive
Vary: Accept-Encoding
Vary: Accept-Encoding
Expires: Wed, 11 Jul 2012 09:44:38 GMT
Cache-Control: max-age=604800
Last-Modified: this works!





James.

On Jul 4, 2012, at 5:56 AM, James Lee wrote:
>    }
>

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

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-----