Mailing List Archive: Caching efficiency, VCL

Caching efficiency, VCL

Sep 20, 2006, 11:32 PM

Post #1 of 3 (573 views)

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Hi all,

installed Varnish during the presentation yesterday, and was playing
with it for most of the evening (together with Marcus, who has
already reared his head on the -dev list). Given the nature of the
site we're trying to serve, there's not much that can be cached
unless we do some serious customizations on the VCL side. That,
combined with some adjustments of the site code, and we should see
some pretty good improvements.

Questions:
- - Others on this list have asked for VCL documentation. I seel the
same.
- - There's also some lack in the documentation of (runtime) parameters
listed in the varnishd man page.
- - Can I control access to the management interface through VCL?
- - Due to the fact that webserver and varnish are currently running on
the same box, I am using a pf ruleset like the following:
no rdr on $int_if proto tcp from $my_ip to $my_ip port 80
rdr on $int_if proto tcp from any to $my_ip port 80 -> $my_ip port 8080
Is this going to limit my performance in any significant way? Given
that I'm running on hardware comparable to what the devs have been
testing on, and the site I'm serving sees only a tiny fraction of the
traffic, I wouldn't think so.
- - The cmdline allows me to specify a minimum ttl for objects -- I'm
missing a way to specify max ttl. Is this something I could do in
VCL, and in that case, why is there an option for the minimum ttl?

I guess that's it for now. Hoping to get a grip of this beast soon!

Thanks,
/Eirik
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Caching efficiency, VCL [ In reply to ]

des at linpro

Sep 21, 2006, 3:05 AM

Post #2 of 3 (544 views)

Permalink

Eirik ?verby <ltning at anduin.net> writes:
> - Others on this list have asked for VCL documentation. I seel the
> same.

I'm working on it.

> - There's also some lack in the documentation of (runtime)
> parameters listed in the varnishd man page.

'param.show -l' in the management interface will give you a complete
list with fairly detailed descriptions.

> - Can I control access to the management interface through VCL?

No.

> - Due to the fact that webserver and varnish are currently running
> on the same box, I am using a pf ruleset like the following:
> no rdr on $int_if proto tcp from $my_ip to $my_ip port 80
> rdr on $int_if proto tcp from any to $my_ip port 80 -> $my_ip port 8080
> Is this going to limit my performance in any significant way? Given
> that I'm running on hardware comparable to what the devs have been
> testing on, and the site I'm serving sees only a tiny fraction of the
> traffic, I wouldn't think so.

Can't you make your web server run on port 8080?

> - The cmdline allows me to specify a minimum ttl for objects -- I'm
> missing a way to specify max ttl. Is this something I could do in
> VCL, and in that case, why is there an option for the minimum ttl?

This is a documentation error - the option actually controls the
*default* ttl if none is provided by the backend server.

You can inspect and modify the TTL in VCL; vcl_fetch would be a good
place to do that... something like:

sub vcl_fetch {
if (obj.ttl > 120s) {
set obj.ttl = 120s;
}
}

(not tested, so caveat emptor)

DES
--
Dag-Erling Sm?rgrav
Senior Software Developer
Linpro AS - www.linpro.no

Caching efficiency, VCL [ In reply to ]

ltning at anduin

Sep 21, 2006, 4:03 AM

Post #3 of 3 (541 views)

Permalink

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On Sep 21, 2006, at 12:05, Dag-Erling Sm?rgrav wrote:

> Eirik ?verby <ltning at anduin.net> writes:
>> - Others on this list have asked for VCL documentation. I seel the
>> same.
>
> I'm working on it.

Good =)

>> - There's also some lack in the documentation of (runtime)
>> parameters listed in the varnishd man page.
>
> 'param.show -l' in the management interface will give you a complete
> list with fairly detailed descriptions.

Ok, my bad. Thanks.

>> - Can I control access to the management interface through VCL?
>
> No.
>
>> - Due to the fact that webserver and varnish are currently running
>> on the same box, I am using a pf ruleset like the following:
>> no rdr on $int_if proto tcp from $my_ip to $my_ip port 80
>> rdr on $int_if proto tcp from any to $my_ip port 80 -> $my_ip port
>> 8080
>> Is this going to limit my performance in any significant way? Given
>> that I'm running on hardware comparable to what the devs have been
>> testing on, and the site I'm serving sees only a tiny fraction of the
>> traffic, I wouldn't think so.
>
> Can't you make your web server run on port 8080?

Yes I can, however as Marcus stated elsewhere, Varnish does not add a
X-Origin-something to the request to the back-end, therefore the back-
end thinks it is in fact the front-end -- and all links etc. are
generated with :8080. Sure this could be fixed, but my pf approach
was the faster way right now.

Plus, the pf approach allows me to have a "failover" - if Varnish is
not running, it will allow the client to connect directly to the back-
end (with some modifications). This is not interesting in all cases,
but in ours it is, and gives us some level of freedom to play around
with Varnish ;)

>> - The cmdline allows me to specify a minimum ttl for objects -- I'm
>> missing a way to specify max ttl. Is this something I could do in
>> VCL, and in that case, why is there an option for the minimum ttl?
>
> This is a documentation error - the option actually controls the
> *default* ttl if none is provided by the backend server.
>
> You can inspect and modify the TTL in VCL; vcl_fetch would be a good
> place to do that... something like:
>
> sub vcl_fetch {
> if (obj.ttl > 120s) {
> set obj.ttl = 120s;
> }
> }
>
> (not tested, so caveat emptor)

Brilliant.

/Eirik

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