Monolithic code architecture significantly limits an organization’s ability to benefit from containerization. Containers are designed to package and run small, modular, loosely coupled services, often following a microservices architecture. CompTIA Security+ SY0-701 explains that containers enhance security by reducing attack surface, improving isolation, and allowing granular patching—but only when applications are designed to support this model.

Monolithic applications bundle all components (UI, business logic, database access) into a single large codebase. This makes it difficult to isolate functions into separate containers, apply least privilege, or patch individual components without redeploying the entire application. As a result, security improvements such as rapid updates, minimal images, and fine-grained access controls are harder to achieve.

Regulatory compliance (A) may add requirements but does not inherently block container use. Patch availability (B) affects maintenance but not architecture suitability. Kernel version (C) can be a constraint, but modern container platforms manage kernel compatibility effectively.

Because containers are best suited for modular applications, monolithic code is the primary limitation, making D the correct answer.