A load balancer is usually the first box you draw after the clients, and the depth you can give on it is a fast proxy for how senior you sound. This covers L4 vs L7, the algorithms and their failure modes, health checks, and the mistake of moving your single point of failure instead of removing it.

Every system wants to be fast, scalable, and reliable, which is exactly why saying so is worthless. This post is about the sharper version: p99 under 200 ms, 99.99% availability, eventual consistency on the timeline — and the architectural lever each of those numbers forces you to pull.

Most system design answers go wrong one step before the boxes and arrows: the candidate never works out how big the system is. Here are the four formulas, the latency numbers worth memorizing, and a worked Twitter example that turns four calculations into five architecture decisions.

Most system design interviews are lost in the first five minutes, not because the candidate lacks knowledge, but because they jump to boxes and arrows before understanding what they are building. Here is the six-step framework that fixes it, and why the order matters more than any individual step.

If you are working with microservices, you are probably already using Docker. Docker is fantastic it packages your application and its dependencies into a single, portable unit. It runs exactly the same on your local machine as it does in production.

But as your system grows, a common question …

If we look at our previous discussion in JWT Dissection, we established that a JWT is effectively a digital ID card. But in a distributed system, an ID card is worthless if anyone can forge it.

In the physical world, we rely on a Gazetted Officer’s Attestation. When we get a document stamped, …