Servers have limits. CPU, memory, bandwidth, open connections, file descriptors. A Denial of Service (DoS) attack doesn't steal anything or run code, it just burns those limits until the service stops keeping up with real users.
Sometimes that's a flood of traffic. Other times it's one cheap request that costs the server a lot. When many machines pitch in, it becomes a Distributed Denial of Service (DDoS).
This module walks through how availability breaks and how small inefficiencies turn into full outages.
