Which design principle most strongly supports scalability?

• A. Documented interfaces and Modular design.
• B. Tight coupling of components.
• C. Hard-coded configurations with no standardization.
• D. Unclear interfaces and no reuse.

Answer: (A)

Scalability comes from building a system that can grow by adding or adjusting parts without rewriting large portions of code. Documented interfaces and modular design achieve this by creating clear boundaries between components and contracts they must follow. When interfaces are well documented, new modules or services can be added, swapped, or scaled independently because everyone knows how to interact with them. Modular design keeps concerns separated, so you can increase capacity for one part of the system without cascading changes elsewhere, and teams can work in parallel without stepping on each other’s toes. This combination also supports reuse and easier maintenance, which are keys to scalable growth.

Tight coupling makes scaling harder because changes in one part force changes in others, creating a ripple effect. Hard-coded configurations with no standardization trap you into rigid, inflexible behavior that’s costly to adapt as demand grows. Unclear interfaces and no reuse prevent assembling additional components or services cleanly, limiting how the system can expand.