如何使用Varnish来加速网站访问

Make Symfony Trust the Reverse Proxy¶

For ESI to work correctly and for the X-FORWARDED headers to be used, you need to configure Varnish as a trusted proxy.

Routing and X-FORWARDED Headers¶

To ensure that the Symfony Router generates URLs correctly with Varnish, a X-Forwarded-Port header must be present for Symfony to use the correct port number.

This port depends on your setup. Lets say that external connections come in on the default HTTP port 80. For HTTPS connections, there is another proxy (as Varnish does not do HTTPS itself) on the default HTTPS port 443 that handles the SSL termination and forwards the requests as HTTP requests to Varnish with a X-Forwarded-Proto header. In this case, you need to add the following configuration snippet:

sub vcl_recv {
    if (req.http.X-Forwarded-Proto == "https" ) {
        set req.http.X-Forwarded-Port = "443";
    } else {
        set req.http.X-Forwarded-Port = "80";
    }
}

If the X-Forwarded-Port header is not set correctly, Symfony will append the port where the PHP application is running when generating absolute URLs, e.g. http://example.com:8080/my/path.

Cookies and Caching¶

By default, a sane caching proxy does not cache anything when a request is sent with cookies or a basic authentication header. This is because the content of the page is supposed to depend on the cookie value or authentication header.

If you know for sure that the backend never uses sessions or basic authentication, have varnish remove the corresponding header from requests to prevent clients from bypassing the cache. In practice, you will need sessions at least for some parts of the site, e.g. when using forms with CSRF Protection. In this situation, make sure to only start a session when actually needed and clear the session when it is no longer needed. Alternatively, you can look into 缓存带CSRF表单的页面.

Cookies created in Javascript and used only in the frontend, e.g. when using Google analytics are nonetheless sent to the server. These cookies are not relevant for the backend and should not affect the caching decision. Configure your Varnish cache to clean the cookies header. You want to keep the session cookie, if there is one, and get rid of all other cookies so that pages are cached if there is no active session. Unless you changed the default configuration of PHP, your session cookie has the name PHPSESSID:

sub vcl_recv {
    // Remove all cookies except the session ID.
    if (req.http.Cookie) {
        set req.http.Cookie = ";" + req.http.Cookie;
        set req.http.Cookie = regsuball(req.http.Cookie, "; +", ";");
        set req.http.Cookie = regsuball(req.http.Cookie, ";(PHPSESSID)=", "; 1=");
        set req.http.Cookie = regsuball(req.http.Cookie, ";[^ ][^;]*", "");
        set req.http.Cookie = regsuball(req.http.Cookie, "^[; ]+|[; ]+$", "");

        if (req.http.Cookie == "") {
            // If there are no more cookies, remove the header to get page cached.
            remove req.http.Cookie;
        }
    }
}

Ensure Consistent Caching Behaviour¶

Varnish uses the cache headers sent by your application to determine how to cache content. However, versions prior to Varnish 4 did not respect Cache-Control: no-cache, no-store and private. To ensure consistent behavior, use the following configuration if you are still using Varnish 3:

Enable Edge Side Includes (ESI)¶

As explained in the Edge Side Includes section, Symfony detects whether it talks to a reverse proxy that understands ESI or not. When you use the Symfony reverse proxy, you don’t need to do anything. But to make Varnish instead of Symfony resolve the ESI tags, you need some configuration in Varnish. Symfony uses the Surrogate-Capability header from the Edge Architecture described by Akamai.

First, configure Varnish so that it advertises its ESI support by adding a Surrogate-Capability header to requests forwarded to the backend application:

sub vcl_recv {
    // Add a Surrogate-Capability header to announce ESI support.
    set req.http.Surrogate-Capability = "abc=ESI/1.0";
}

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 Symfony adds automatically:

Cache Invalidation¶

If you want to cache content that changes frequently and still serve the most recent version to users, you need to invalidate that content. While cache invalidation allows you to purge content from your proxy before it has expired, it adds complexity to your caching setup.