Most system design resources focus on interview preparation — how to design Twitter in 45 minutes, how to draw boxes and arrows convincingly. This article is different. These are the concepts I wish I had internalized earlier because they changed how I approach every technical decision, including the ones I make building TokenPulse.
The fundamental trade-off: consistency vs availability
The CAP theorem states that a distributed system can guarantee at most two of three properties: Consistency, Availability, and Partition tolerance. Since network partitions are unavoidable in real systems, the practical trade-off is between consistency and availability.
Consistency means every read receives the most recent write. If user A writes data and user B immediately reads it, B sees A's write.
Availability means every request receives a response — not necessarily the most recent data, but a response.
