Varnish and FLV streaming

When doing usual website speed optimization to a website that has lots of videos, I have encountered a problem. Videos started breaking for no apparent reason, they loaded very slowly and in general were unusable.

It turned out it was because of two things. One was that Apache has been set up to compress everything except images with mod_deflate - this does not play well with streaming. Another problem was that Varnish running in front of the web server wasn't set up to do streaming, so it first fetched whole video to its cache and then sent it to the browser. It was slow.

The solution was to upgrade Varnish to 3.0.1 and add the following code to vcl_fetch:

if(beresp.http.Content-Type && beresp.http.Content-Type ~ "video") {
        set beresp.do_stream = true;
}

Optimizing website performance is not an easy job and has tons of catches like this.Order optimization now!