Concept
Distributed Systems
A distributed system is a system made of independent components that communicate over a network to behave like one useful whole.
Distributed systems are difficult because the network turns coordination into an engineering problem. Messages can be delayed, duplicated, reordered, or lost. Machines can fail independently. Observers can disagree about what happened.
The durable lesson is not that distributed systems are impossible. It is that their behavior cannot be understood by inspecting one component alone.