Building Resilient Software: 10 Guidelines I Swear By

1. Fail Fast, Fail Loud

Validate inputs at the boundary. Throw early with clear messages. Silent failures become 3am bugs.

2. One Way to Do a Thing

Consistency reduces cognitive load. If you have two patterns for the same concern, delete one.

3. Logs Are Your First Debugger

Before adding a debugger, check the logs. If the logs are useless, fix the logs first. Structured logging with correlation IDs pays for itself in the first incident.

4. Dependencies Are Liabilities

Every library you add is code you don’t control. Before npm install, ask: can I do this in 20 lines? The answer is often yes.

5. Test Behavior, Not Implementation

A test that breaks on every refactor tests the wrong thing. Test the interface contract, not the internal variable.

6. Handle Partial Failure

Services degrade, databases lag, APIs return 500s. Your code should handle the case where one thing fails but everything else keeps working.

7. Make Illegal States Unrepresentable

Use types to encode invariants. If a field can’t be empty, don’t use a string — use a branded type or a dedicated class.

8. Prefer State Machines Over Booleans

Two booleans (isLoading, isError) have four states but only three are valid. A state machine (idle | loading | success | error) has four and all are valid.

9. Measure Before Optimizing

The slowest part of your app is never what you think. Profile before optimizing. Then profile again.

10. Write Code to Be Deleted

The best code is the code you can delete without worrying. Small functions, clear interfaces, and zero magic. Delete freely.