Apologies if the following is in not what you are asking.So what exactly is the attack? Looks like Cloudflare is one of the end providers for the Apple Relay service. Is this merely a case of your hosting solution not being able to handle excessive connections?
What is a DDOS attack? In essence, an overwhelming influx of data/page requests. In actuality, they involve a wide array of 'zombie' devices that make ping the servers. These typically include devices with weak security - things like household appliances such as washing machines, switches, alarm clocks, etc. They also include audio equipment as these devices have some of the weakest security. These devices get hacked and then lie in waiting to be woken up so they can ping the target. The reason for the wide array of devices is so that the ISP cannot block service to any one source making data/page requests.
Why does a website like WBF get affected even if they are not the target? Because the ISP or other related service get hammered so significantly, they often respond by throttling traffic across their clients. They do this so nobody actually becomes unavailable. But, many services get slowed down.