6.4Development processes and DevOps

The choice of development process and post-release maintenance operations shape the system's entire lifecycle. A systems architect is responsible for judging, from constraints such as how firm the requirements are and how fast they change, whether waterfall or agile fits better, and for routing post-release incidents, requests, and environmental changes to the appropriate response based on the four maintenance categories. Misclassifying this can lead to incidents such as an issue needing urgent attention getting buried among unplanned enhancement work and deprioritized.

6.4.1Waterfall, iterative, and agile

• The waterfall model proceeds through requirements definition, design, implementation, and testing in sequence from upstream to downstream, with the assumption of no going back. For large systems whose requirements are settled early and change little, it has the advantage of being easy to manage for progress and budget, but its weakness is that a requirement change late in the process incurs large rework cost.
• Iterative development repeats the whole sequence from requirements through implementation and testing in small units (iterations), incorporating feedback each time and building up functionality incrementally. Agile (a leading example being Scrum) is a practical form of this, producing working software every short period (a sprint) and flexibly following changes in priority or requirements. It suits projects where requirements change frequently and early value delivery matters.