1.Architecture

Architecture as system-level decisions about boundaries, dependencies, deployment, data, quality attributes, and evolutionary trade-offs.

Choosing monolith, layered, event-driven, microservice, read/write split, and domain-oriented patterns from constraints rather than fashion.

A single deployable application and the trade-offs between operational simplicity, modularity, scaling, and organizational boundaries.

Separating presentation/application/domain/infrastructure responsibilities while controlling dependency direction.

Separating write authority from read replicas/projections and handling replication lag, read-your-writes, routing, and failover.

Producing and reacting to events with asynchronous coupling, delivery semantics, ordering, idempotency, and observability.

DDD concepts: bounded contexts, ubiquitous language, aggregates, entities, value objects, domain services, and context integration.

Independently deployable service boundaries with explicit data ownership and the distributed-systems/operational costs they introduce.