Adobe Commerce Architecture and Solution Design
Architecture questions test whether you can map a business requirement onto the layered Commerce stack and justify tradeoffs. Know the layers: presentation (themes, PWA storefront), service contracts and API surface, application (modules, plugins, preferences), persistence (repositories, resource models), and infrastructure (Cloud, search, cache, queue). The service contract layer is the conceptual center: business logic should be reachable through interfaces declared in Api namespaces, and interdependencies between modules should flow through those contracts rather than concrete classes.
Expect traps around where customization belongs. A question may propose editing a vendor module directly; the correct answer is almost always a plugin, preference, or a new module that composes rather than patches. Watch for confusion between plugins (around public methods) and preferences (replace a class globally), and between observers (react to events) and plugins (intercept behavior). Also distinguish B2B vs B2C feature sets and Commerce vs Open Source edition capabilities.
Worked example
A requirement: "Apply a loyalty discount to the cart total without breaking third-party tax modules." Rule of thumb: prefer the narrowest interception point that is still stable. If the discount is a total collector, implement a new CollectorInterface total rather than rewriting the quote total model, so other collectors still run. If it must alter an existing public method's output, a plugin after method is safer than a preference because it preserves the original class and other plugins.
Solution design questions reward answers that name the extension point, the layer it touches, and the upgrade impact.