I've got Varnish (3.0.3) sitting as a load-balancer/static cache in front of two web servers. I've got a CDN set up using Original Pull method. If I grab a URL from an image on my site manually, drop in the CDN address, I can verify that original pull is working and the image is pulled to the CDN and served.
My application is fairly complex and I'm testing this CDN to see if it significantly speeds up the web app, so I don't want to rewrite any of my php code to use the CDN images just yet.
What I'd like to do is set Varnish up to rewrite requests received for image files and pull them through the CDN instead of from the two Apache servers directly in my cluster.
I've read through the Varnish documentation and a couple howto's online about doing something similar, but I just can't get it to work properly and need a little help here.
Here are a couple different ways I tried doing this (edited for brevity):
sub vcl_recv {
#if request is image, redirect to CDN
if (req.url ~ "\.(gif|ico|jpg|jpeg|png)$") {
set req.http.host = "cdn.domain.com/";
error 750 req.http.host + req.url;
}
}
sub vcl_error {
if (obj.status == 750) {
set obj.status = 302;
set obj.http.Location = obj.response;
return(deliver);
}
}
That didn't work. It resulted in broken images everywhere, and anything that did show up was using the .webp extension, so it wasn't being processed by the condition above.
So I tried this:
backend cdn {
.host = "cdn.domain.com";
.port = "80";
}
sub vcl_recv {
#if request is image, redirect to CDN
if (req.url ~ "\.(gif|ico|jpg|jpeg|png)$") {
set req.backend = cdn;
return(lookup);
}
}
This showed some images on the page, but when viewing their source, they looked to be coming from the Apache servers (the domain name wasn't that of the CDN) and only about half the images were displaying...probably browser cache.
I'd love some input here, thanks guys.
Is there no way to use Varnish for this kind of redirect? Would I be better off setting nginx up in front of Varnish to rewrite requests to the cdn?
UPDATE: Using both answers given below, I have the redirect working and an ACL in place to allow the CDN to pull images directly vs redirecting to itself. However, though I verified the ACL is allowing connection through by using my own external IP, the CDN isn't pulling new images from the server. It gives a 502 error (odd<) instead of pulling the image from the local server to the CDN and serving it. This is what the block of my vcl_recv looks like now:
acl cdn {
"ip.of.CDN";
}
sub vcl_recv {
#if request is image, redirect to CDN
if (req.url ~ "\.(gif|ico|jpg|jpeg|png)$") {
if(!client.ip ~ cdn){
error 750 "http://cdn.domain.com" + req.url;
}
}
}
sub vcl_error {
if (obj.status == 750) {
set obj.status = 302;
set obj.http.Location = obj.response;
return(deliver);
}
}