Reliable, Scalable, and Maintainable Applications

Reliability

The system should continue to work correctly even in the face of adversity. This means hardware faults, software faults, and human errors.

• Hardware faults: add redundancy (disks, power, servers)
• Software faults: isolate failures, test thoroughly, monitor
• Human errors: good UX, sandbox environments, quick rollback

Scalability

As the system grows in data volume, traffic, or complexity, there should be reasonable ways of dealing with that growth.

• Measure load with a load parameter (requests/sec, data size, etc.)
• Performance metrics: throughput, response time percentiles

Maintainability

Three ingredients:

1. Operability: easy to keep running
2. Simplicity: easy for new engineers to understand
3. Evolvability: easy to change

Martin Kleppmann argues that removing accidental complexity is the main battle.