Most of us are building distributed systems. This is a fact. According to Wikipedia, a distributed system is a system whose components are located on different networked computers, which then communicate and coordinate their actions by passing messages to each other. A distributed system could either be a standard three-tier web application or it could be a massive multiplayer online game.
The goal of a distributed system is to solve a problem that can’t be solved on a single machine. A single machine can’t provide enough compute or storage resources required to solve the problem. The user of a distributed system perceives the collection of autonomous machines as a single unit.
The distributed systems are complex as there are several moving parts. You can scale out components to finish the workloads in a reasonable time. Because of numerous moving parts and their different scaling needs it becomes difficult to reason out the characteristics of a distributed applications. CAP theorem can help us.