In this week's 2-Minute Tech Tuesday, we'll be discussing banning, which is a mechanism in Varnish to remove outdated content from the cache so that new content can be presented immediately, rather than waiting for the cache to expire.

It's cargo-cult fighting time! Today, we are going to look at a ban expression that you probably have used, and maybe even have recommended (gasp!) to your fellow Varnish users:

req.url ~ /

We'll discuss why we use it, why it's good but mostly bad, and how to fix it. Hopefully, along the way, we'll shed some light on some Varnish internals that you can use in other situations.