What is agile architecture?

June 25, 2014

Agile ArchitectureArchitecture is a high level view of a system in the context of its environment, dependencies, technology, structure and behavior.

Architecture must be solid, useful and beautiful.

Software architecture is typically hard to define as the term software architecture is used to describe many facets of software structure, behaviour, design, activity and documentation. The concept of software architecture is also relevant at different levels of a system as the components of one system become a reusable platform for the next system. Ultimately the emergent behavior caused by layers of architectural dependencies and reuse can be difficult to predict.

Architecture is a simplification of the system, used to communicate the nature of that system and guide its development. However, architecture is more than just a diagram, it is grounded in technical context describing technology stacks, standards adopted, common ways of doing things (mechanisms), how non-functional requirements are met and the elements that will meet functional requirements. Architecture provides a shape and look and feel to the internals of a system that are the foundation for the ultimate external behavior.Da Vinci's Virtuvian Man

The idea of an “Architect” role with such a broad focus is analogous to that of a structural architect concerned with buildings. Indeed in 25 BCE Vitruvius (a well known Roman writer and architect who inspired Leonardo Da Vinci, hence the Vitruvian Man ) described an architect as:

The ideal architect should be a man of letters, a mathematician, familiar with historical studies, a diligent of philosophy, acquainted with music, not ignorant of medicine, learned in the responses of jurisconsults, familiar with astronomy and astronomical calculations.

Virtuvius is famous for stating that architecture must be solid, useful, beautiful (De architectura). The same three qualities relate to software architecture. Despite architecture being a fine balance between a subtle science and an exact art we must realise it is only useful if it is aligned to requirements and becomes executable.

Architecture, not documentation

In line with one of the founding Principles of Holistic Software Architecture I:

Value working software in the form of quality releases from short development cycles over comprehensive documentation, business analysis and enterprise architecture documentation.

Choosing how much architectural work is necessary up-front and especially how much architectural documentation is necessary is difficult.

Traditional document focused development methods promoted large up-front effort to detail, in document or model form, the architecture and system design prior to development. As well as the inherent risk extension issues in waterfall processes this could often cause “analysis paralysis” where architecture work was seen as an endless diagram drawing exercise.

Agile methods focus on working software over documents and designs, however this doesn’t mean that no documents or designs should be produced. It is almost always useful to have some description of an architecture before development even if it’s just a statement that the team’s usual architecture will be used as otherwise team members won’t even know which language to start writing in.

Good architecture addresses how we’ll resolve the major technical risks, communicates between the team the overall structure of the solution and works out how our solution will meet the functional and non-functional requirements. Knowing when we’ve worked out enough architecture so that we’ve reduced the complexity of the problem into manageable sizes for the team is a difficult challenge.

Levels of architectural formality

Doing too much architectural analysis or elaboration, either through abstract design and modelling or practical spiking (writing small amounts of throwaway code to demonstrate the feasibility of a technical approach or architectural idea) will slow down a development project and increase the risk of wasted work. Value is only achieved once working systems are in the hands of the customers/users.

Alternatively not doing enough architectural analysis can lead to significant architectural refactoring during a projects lifetime, as key requirements can’t be met based on the current architecture, again leading to wasted work and slowing down the project.

When doing up front architecture, especially in the form of documents and models, we need to be careful to consider architectural work in the context of the team’s definition of done. Typical levels of done don’t normally include “analysed”, “architected” or “designed”. Although these terms might be meaningful to describe internal team development states they do not constitute working software and are only a step on the way to creating value.