When building a software system, engineers recognize three fundamental truths:

1. All software has an architecture, whether it is designed and implemented intentionally, or it emerges by coincidence.
2. System complexity grows over time as requirements shift, use cases evolve, team members come and go, and technologies advance.
3. Without deliberate management of the system’s evolution, its architecture may stray from its original objectives and blueprint, leading to unintended architectural drift.

Architectural drift can affect any application, irrespective of its initial architectural style or the quality of its original design.

After all, the ease of making changes to a system has significantly increased compared to the past. Gone are the days when you had to phone your hardware rep to order a new server, confirm that there was rack space for it in the data center (i.e. basement), configure it, integrate it into the network, and migrate data into it. Nowadays, a few clicks in a cloud vendor console or a commit to Infrastructure as Code (IaC) can redefine your application’s architecture in mere minutes.

Engineers not only face the challenge of adapting to continuously evolving system architectures but also grapple with the shifting role of software architecture within agile teams and the lack of visibility into the architectural decisions made by other teams.

This leads to a vicious cycle where architectural drift makes the system increasingly difficult to comprehend and modify. Developers find it challenging to implement changes without causing unintended side effects or disrupting existing functionalities, which leads to further architectural drift.

As a result, development cycles lengthen, costs rise, and overall productivity declines.

Understanding the root causes, consequences, and strategies for managing system architecture drift is vital. This blog post aims to provide a comprehensive exploration of architectural drift, including its definition, underlying causes, consequences, and effective mitigation techniques.

The What and Why of System Architecture Drift

System architecture drift falls under the broader category of Architectural Technical Debt, which encompasses all the intentional and unintentional decisions made during the system design process (e.g. architectural style, tech stack, development methodologies, etc.), that result in issues such as reduced maintainability, increased complexity, decreased performance, and scalability challenges.

Specifically, Architectural Drift refers to the gradual deviation of a system’s architectural design from its original or intended architecture due to ad-hoc alterations and additions.

Imagine that you’re building a house designed in the Mediterranean style, complete with characteristic clay tile roofing, stucco walls, and wrought iron balconies. Suppose, partway through, you decide to incorporate a Gothic-style round turret to accommodate your astronomy hobby. Later, to cater to your growing family, you might add a post-modern extension. What began as a cohesive design evolves into a disjointed amalgamation of styles.

This analogy mirrors the reality in software architecture: the system may start with a clean architecture but evolve into a complex tangle of multiple architectural paradigms, inconsistent coding practices, redundant components, and tangled dependencies due to uncoordinated additions and modifications.

There are various reasons behind system architecture drift:

Adapting to Evolving Needs: Architectural adaptations are often intentionally made to align with changing requirements or evolving business needs. Software systems are dynamic entities, and architectural drift can sometimes reflect an organization’s commitment to rapidly delivering new functionalities, meeting customer demands.

Unclear Architectural Governance: Development teams lack a defined architecture, guidelines, or principles to guide their work. This lack of direction can lead to ad-hoc decision-making and improvisation, contributing to architectural drift.

Result of Architectural Technical Debt. Compromises, shortcuts, and errors made during development can have a knock-on effect on other architectural decisions. Examples of ADT issues that influence future choices:

• Re-inventing the Wheel: Choosing custom-built components over existing solutions with similar functionality (e.g. building your own persistence library).
• Permanent MVPs. A temporary, “bare-bones” solution becoming an integral part of the system’s architectural foundation (e.g. adopting prototypes of a new architecture, immature R&D components, experimental development branches, etc.).
• Persistent Workarounds. A temporary workaround, implemented to bypass some architectural constraints, becoming deeply embedded into the architecture.

Inadequate Collaboration. Poor collaboration within and between teams can exacerbate architectural drift. Without a shared understanding or visibility into the overall system architecture and modifications made by other teams, disjointed efforts can lead to increased fragmentation and inconsistency in the system’s architecture.

Architectural drift ultimately builds over time due to a multitude of factors — different business needs, architectural directions, rogue spinoffs — resulting in increased system complexity and creating a less maintainable and cohesive architecture.

What's Next

For more about system architecture drift check out these next articles:

• 101 on Architectural Technical Debt
• [Part 2] Architectural Drift in Real Life Systems
• [Part 3] The Temptation to Ignore Architecture Drift
• [Part 4] Effective Measures to Control System Architecture Drift

Thank you for reading! 💜