Loosely Coupled Architecture
Loosely Coupled Architecture refers to designing systems where components or services can evolve, deploy, and fail independently.
It enables agility, resilience, and scalability — allowing teams to iterate rapidly without excessive coordination or risk.
Level 1 – Initial (Ad Hoc)
Architecture is tightly coupled and monolithic.
Changes in one component often require coordinated changes in others, creating bottlenecks and instability.
- Services or modules are highly interdependent
- A single failure can cascade across systems
- Code changes require coordination across multiple teams
- Releases are risky and infrequent due to entanglement
- Technical debt and complexity grow unchecked
Level 2 – Managed (Emerging Practice)
Teams begin modularising the system, introducing some separation of concerns and encapsulation.
- Components are logically separated but not deployable independently
- Teams start exploring microservices or modular monoliths
- Some interfaces exist, but contracts are unstable
- Cross-team coordination is still required for many changes
- Dependency management is emerging but fragile
Level 3 – Defined (Standardised)
Architecture is modular and aligned to domain boundaries.
Teams can develop and deploy independently using well-defined interfaces.
- Systems follow domain-driven design or similar decomposition patterns
- APIs and contracts are clearly defined and versioned
- Teams are responsible for the full lifecycle of their services
- Integration points are standardised and loosely coupled (e.g. event-driven, REST, GraphQL)
- Failures in one area are isolated and do not cascade system-wide
Level 4 – Quantitatively Managed (Measured & Controlled)
Architecture is designed and evolved based on metrics related to coupling, reliability, and flow.
- Metrics include deployment frequency, time-to-recover, change lead time, and blast radius
- Teams track and manage dependencies explicitly
- Architectural decisions are informed by data (e.g. service latency, failure rate)
- API changes follow versioning and deprecation policies
- Architectural fitness is reviewed through regular technical governance
Level 5 – Optimising (Continuous Improvement)
The architecture continuously evolves to support flow, autonomy, and resilience.
Teams can safely innovate at speed, and architectural boundaries enable scale.
- Teams experiment with new patterns (e.g. event-driven, serverless, edge computing)
- Feedback loops from production drive architectural evolution
- Services are observable, fault-tolerant, and adaptive to change
- System health and architectural drift are continuously monitored
- Architecture empowers organisational agility and product innovation