How does Varnish cache handle different domains?

Question

I just started reading about Varnish and am considering using it as a frontend to my webservers. I have multiple domains on my webserver that fetch the same content when the same query strings are used. So lets say one client visits:

http://domain1.com/script.php?string1=abc&string2=123 

And later on, someone else visits:

http://domain2.com/script.php?string1=abc&string2=123 

Would Varnish cache the results from the first visit and use that for the second client? Thanks!

EDIT: After some more reading, it sounds like the following may work:

sub vcl_hash { set req.hash += req.url; return (hash); } 

So instead of added the http.host variable to the hash, it ignores it.

Answer 1

You can configure it to do so, sort-of. By default, it won't (and shouldn't).

From Varnish FAQ/HowDoI

I have a site with many hostnames, how do I keep them from multiplying the cache?

You can do this by normalizing the "Host" header for all your hostnames. Here's a VCL example:

if (req.http.host ~ "^(www.)?example.com") { set req.http.host = "example.com"; }

Answer 2

I have 3 domains on my VM, I am using Nginx and Varnish, currently I am on a pre prod configuration, here what I am doing :

NGINX:80 ==> VARNISH:8080 ==> NGINX:8081 

I am using Nginx:80 like a proxy IF the domain needs Varnish, if not, I use FastCGI stuff. In this exemple, the not Varnish sites are not concerned by Varnish. It looks stupid but it woks ;-) and none of my customers complain (yet....).