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.