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How to use Varnish to speed up my Website
How to use Varnish to speed up my Website¶
Because Symfony2’s cache uses the standard HTTP cache headers, the Symfony2 Reverse Proxy can easily be replaced with any other reverse proxy. Varnish is a powerful, open-source, HTTP accelerator capable of serving cached content quickly and including support for Edge Side Includes.
Configuration¶
As seen previously, Symfony2 is smart enough to detect whether it talks to a reverse proxy that understands ESI or not. It works out of the box when you use the Symfony2 reverse proxy, but you need a special configuration to make it work with Varnish. Thankfully, Symfony2 relies on yet another standard written by Akamaï (Edge Architecture), so the configuration tips in this chapter can be useful even if you don’t use Symfony2.
Note
Varnish only supports the src attribute for ESI tags (onerror and
alt attributes are ignored).
First, configure Varnish so that it advertises its ESI support by adding a
Surrogate-Capability header to requests forwarded to the backend
application:
1 2 3 | sub vcl_recv {
set req.http.Surrogate-Capability = "abc=ESI/1.0";
}
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Then, optimize Varnish so that it only parses the Response contents when there
is at least one ESI tag by checking the Surrogate-Control header that
Symfony2 adds automatically:
1 2 3 4 5 6 7 8 9 10 | sub vcl_fetch {
if (beresp.http.Surrogate-Control ~ "ESI/1.0") {
unset beresp.http.Surrogate-Control;
// for Varnish >= 3.0
set beresp.do_esi = true;
// for Varnish < 3.0
// esi;
}
}
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Caution
Compression with ESI was not supported in Varnish until version 3.0 (read GZIP and Varnish). If you’re not using Varnish 3.0, put a web server in front of Varnish to perform the compression.
Cache Invalidation¶
You should never need to invalidate cached data because invalidation is already taken into account natively in the HTTP cache models (see Cache Invalidation).
Still, Varnish can be configured to accept a special HTTP PURGE method
that will invalidate the cache for a given resource:
1 2 3 4 5 6 7 8 9 10 11 12 | sub vcl_hit {
if (req.request == "PURGE") {
set obj.ttl = 0s;
error 200 "Purged";
}
}
sub vcl_miss {
if (req.request == "PURGE") {
error 404 "Not purged";
}
}
|
Caution
You must protect the PURGE HTTP method somehow to avoid random people
purging your cached data.
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.