Boil the cloud down to a single sentence and it's "renting someone else's computer." But there isn't just one way to rent that "computer." You can rent an entire virtual server, you can drop off a snippet of code and rent runtime only when it executes, or you can rent by the container. Those three approaches are EC2, Lambda, and ECS/Fargate, respectively. The CLF-C02 exam doesn't go deep on any of the three, but it will absolutely ask "which compute do you pick in which situation."
Today we'll lay out what problem each of these three compute services was born to solve, and how they line up along a single axis: "how much operational responsibility you hand off to AWS."