Page Speed: Leverage proxy caching

Page Speed recommends:

Don't include a query string in the URL for static resources

Most proxies, most notably Squid up through version 3.0, do not cache resources with a "?" in their URL even if a Cache-control: public header is present in the response. To enable proxy caching for these resources, remove query strings from references to static resources, and instead encode the parameters into the file names themselves.

Don't enable proxy caching for resources that set cookies

Setting the header to public effectively shares resources among multiple users, which means that any cookies set for those resources are shared as well. While many proxies won't actually cache any resources with cookie headers set, it's better to avoid the risk altogether. Either set the Cache-Control header to private or serve these resources from a cookieless domain.

Be aware of issues with proxy caching of JS and CSS files

Some public proxies have bugs that do not detect the presence of the Content-Encoding response header. This can result in compressed versions being delivered to client browsers that cannot properly decompress the files. Since these files should always be gzipped by your server, to ensure that the client can correctly read the files, do either of the following:

• Set the the Cache-Control header to private. This disables proxy caching altogether for these resources. If your application is multi-homed around the globe and relies less on proxy caches for user locality, this might be an appropriate setting.
• Set the Vary: Accept-Encoding response header. This instructs the proxies to cache two versions of the resource: one compressed, and one uncompressed. The correct version of the resource is delivered based on the client request header. This is a good choice for applications that are singly homed and depend on public proxies for user locality.

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