There must be a careful balance between redundancy and capacity, and what systems you need to account for which are ultimately out of your control. DDoS mitigation services measure defensive capacity against attacks in in in Gigabit Per Second (Gbps) or Terabit per Second (Tbps) Another type of DDoS attacks require a reverse proxy architecture to intercept, inspect, validate, and pass along traffic from a network of reverse proxies back onto the origin web server environment. When it comes to outages, which ISP outages can originate, this path is not always represented by the path their traffic takes.
Source: https://threatpost.com/finding-beauty-in-the-architecture/146167/