By now, you’ve explored the core principles that make modern distributed systems scalable, reliable, and observable.

You’ve learned:

• how to estimate system capacity using Little’s Law
• design efficient load balancers, pick shard keys
• tune caching layers
• handle message delivery semantics
• reason about consistency and fault tolerance

More importantly, you’ve developed the ability to analyze trade-offs, the key skill interviewers look for when evaluating real-world design thinking.

With this foundation, you can confidently approach system design interviews and make better architectural decisions in production systems.

You now understand how individual concepts, from replication and caching to error budgets and observability, fit together to form resilient, high-performance services.