A distributed denial of service (DDoS) attack can be a real nightmare for network administrators. Attackers send malicious commands to an application from a huge number of sources, often compromised computers all over the world, in an attempt to disable the application. Individually, the requests might seem innocuous, as it might be something like asking for the contents of a single web page. But, on aggregate, the requests can put enough of a strain on servers to bring an application to its knees.

Since the requests originate from so many sources all over the world, it's not as simple as configuring an access control list (ACL) to block the traffic. To mitigate these types of attacks, you need a much more intelligent and reactive service. AWS Shield does this job for you, and comes in two varieties—AWS Shield Standard and Advanced.