A decade after microservices became mainstream, the pattern is well-understood in theory and still routinely misapplied in practice. Here is what the field actually knows and where teams still get it wrong.
When AI can write the code, the decisions that matter most are the ones that happen before the code is written. System design was always important. Now it is the primary leverage point.
The design decisions that make APIs a pleasure to work with years later - consistency, clear contracts, thoughtful versioning, and the mistakes that are expensive to undo.
What microservices actually cost, what problems they actually solve, and how to think about the decision instead of treating it as a default choice.
Five principles that show up in every serious codebase - explained through violations you will recognize, not textbook abstractions.
Three patterns that appear constantly in real codebases - what problem each solves, what the structure looks like, and where you have already seen them.
Three more patterns from the everyday toolkit - adding behavior without inheritance, bridging incompatible interfaces, and treating actions as objects.
