Software Architecture — Design for Scale

Software architecture defines the high-level structure of a software system: how it is decomposed into components, what the interfaces between components are, and how the system meets non-functional requirements (performance, reliability, maintainability, scalability). Good architecture makes it easy to change the parts that need to change and stable in the parts that must not change.

Why companies use it

·Architecture decisions are the most expensive to change later — getting them right early saves enormous rework cost
·A clear architecture enables parallel team development by defining stable interfaces that teams can code against independently
·Non-functional requirements (response time, memory footprint, safety integrity level) cannot be met without deliberate architectural choices
·In embedded and real-time systems, RTOS task structure, interrupt priorities, and memory layout are architectural decisions with direct impact on system correctness

What hiring managers look for

·Senior software engineers are expected to propose and defend architectural decisions, not just implement features
·Familiarity with common architectural patterns (layered, event-driven, microservices, client-server, publish-subscribe) is expected
·The ability to draw and communicate a system architecture diagram concisely is a key senior engineer skill
·In safety-critical embedded software, architecture choices directly affect the achievability of functional safety requirements (SIL/ASIL level)

Typical interview questions

What is the difference between software architecture and software design?

Describe an architectural pattern you have used and explain why it was appropriate for that system.

How would you architect a real-time data acquisition system that must process sensor data at 100 kHz with 1 ms latency?

What is the difference between a monolithic architecture and a microservices architecture? When would you choose each?

How do you document a software architecture? What views and diagrams do you produce?

Common mistakes

·Over-engineering architecture for anticipated future requirements that never materialise — YAGNI (You Ain't Gonna Need It) applies to architecture too
·Ignoring non-functional requirements (latency, memory, power consumption) when choosing architecture — these often constrain the entire design more than functional requirements
·Not defining interface contracts between components — teams building against undefined interfaces produce incompatible implementations
·Choosing a fashionable architecture (microservices) for a system where a simpler architecture (modular monolith) would better fit the team and problem
·Not revisiting the architecture as requirements evolve — architecture that was right for v1 may be wrong for v3

Real engineering example

A motion control software team chose a layered architecture (hardware abstraction → real-time control → application logic) for a new servo drive firmware. This allowed the real-time control layer (IEC 61131-3) to be developed and certified independently from the application layer (C++), and the hardware abstraction layer to be mocked for unit testing. When the customer changed the target processor mid-project, only the hardware abstraction layer needed to be rewritten — the upper two layers were unchanged. The decoupling saved an estimated 8 weeks of rework.

Topics covered

software architecturedesign patternsmicroserviceslayeredreal-timeRTOSembedded

Related interview guides

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