Painful Varnish Mistakes

This post was initially titled “Top 6 Varnish mistakes," to echo Espen’s blog. Even though his material is three years old, the content is still relevant. Plus, there’s a healthy colleague competition going on here, and I can’t just mimic Espen if I hope to beat him, so I had to do something different. Instead, I’m going to compete on brutality: this post isn’t about explaining the most common mistakes, but rather the ones that can really kill your service, one way or another. I know it sounds a bit scary, and it is, but that’s for your own good, really. So buckle up, and let’s see what I have in my Little Shop of Errors.
If your installation started with Varnish 4.0+ AND you followed Espen’s advice to not trust everything you read on the interwebz, you are probably safe. On the other hand, if your installation was migrated from Varnish 3.0, have a very careful look at your Varnish command line and search for thread_pool_add_delay. More lazily, if