Carving Sustainability into Software Architecture

Today's digital society puts substantial demands on natural resources, including energy, water, and raw materials, while also challenging our societal values like fairness or privacy. As a result, these demands have led to sustainability concerns in software development and operation, evolving from an emerging consideration into a fundamental responsibility. Rethinking the traditional way of how we design and implement software-intensive systems is necessary. Current research shows that organizations and software engineers are aware of the new concerns and recognize developing legislation and consumer demands, yet they experience uncertainty on how to face them within daily work. While both research and practice make incremental advances on the product level, e.g., by choosing a more energy efficient programming language, or protecting against social bias in AI software, those attempts remain largely as an afterthought. Insights are necessary on how to architect for software sustainability up from the beginning in the software development lifecycle. The objective of this thesis is therefore to explore how sustainability concerns can be addressed within current software architecture practice. In order to address this problem statement, we apply rigorous research methods while collaborating with multiple industry partners across different domains. We derive empirical evidence based on qualitative research methods in form of interview and questionnaire surveys involving more than 85 practitioners, four independent focus groups, one Delphi study comprising eleven experts, a rapid review screening 16 secondary studies, and five quantitative experiments with three real-world cloud-based applications. The results of this dissertation present novel insights in the current processes of software architecture work, methods on how these existing processes can be facilitated and reused for sustainability, and proposals for new approaches tackling sustainability concerns. As all our results are derived with close industry involvement, we hence ensure their practical relevance.