In this week’s episode of Two-Minute Tech Tuesday, we'll talk about UDO which is short for "Unified Director Object".

This week's episode is about load balancing, which is a concept where traffic load gets distributed to a collection of underlying servers using an algorithm to ensure equal distribution.

There's a recurring discussion I get myself into, and it goes roughly like this:

- I want to stream live video, what kind of machine, and how many of them do I need?
- It depends.
- Depends on what?
- Math! Also, numbers!
- ...
- Joking, can you tell me <list of characteristics>
- <provides value>
- <performs black magic>. The answer to your question is <scarily accurate values>!

Obviously, it doesn't go "exactly" like this, but the goal of this post is going to be largely about boring math, so it sounds cooler if we say I'll be talking about black magic, right?

Let's open the grimoires and see how we can answer this sizing question!

In this post, I will explain how to create a highly available, self-routing sharded Varnish Cache cluster. This is similar to a standard sharded cluster with one exception, there is no dedicated routing tier. Each node in the cluster can route the request to the proper destination node, by itself.