Strategic DDD: The Art of Customer-Supplier Relationships

Welcome to our exploration of Domain-Driven Design's strategic patterns! In this post, we'll dive deep into the Customer-Supplier relationship pattern, a more formalised version of team interactions in bounded contexts.

Understanding Customer-Supplier

Think of this relationship like a professional service agreement between two departments. Unlike the pure upstream/downstream pattern, the supplier actively considers the customer's needs when planning changes. It's a relationship built on negotiation, clear expectations, and mutual understanding of requirements.

Detailed Analysis

The Customer-Supplier relationship formalises interactions through clear service agreements and negotiated interfaces. This pattern creates a more balanced dynamic where the supplier team often negotiates with the customers needs when planning changes. This collaborative approach helps ensure that both contexts evolve in a coordinated way while maintaining clear responsibilities and boundries.

Architectural Dimensions:

• Coordination Model: Supports both orchestration and choreography, depending on the service agreement. Orchestration is common for complex workflows, while choreography works well for loosely coupled services.

• Communication Model: Typically implements a mix of synchronous calls for immediate service requests and asynchronous patterns for background processes and notifications.

• Consistency Model: Usually requires atomic consistency for critical operations, with eventual consistency acceptable for non-critical updates and notifications.

Perfect for:

• Business-critical integrations

• Formal service agreements

• Well-defined domain boundaries

• Core business services

• Regulated interfaces

• Contract-driven development

• Professional services

NFR Alignment:

• Reliability: ⭐⭐⭐⭐⭐

• Availability: ⭐⭐⭐⭐⭐

• Maintainability: ⭐⭐⭐⭐

• Security: ⭐⭐⭐⭐

Real-world Examples:

1. A billing service (supplier) providing invoicing capabilities to multiple product lines (customers)

2. Report generation service (supplier) serving multiple business units with specific reporting needs

3. Data analytics platform (supplier) providing insights to various department systems (customers)

4. Identity management service (supplier) with negotiated SLAs for different internal products

Tradeoffs & Challenges

Architectural Challenges:

• Complex service level agreements to maintain

• Need for comprehensive API versioning strategies

• Careful contract management and evolution

• Integration testing complexity across boundaries

• Managing multiple service versions simultaneously

• Balance between standardisation and customisation

• Performance optimisation for various usage patterns

Organisational Impacts:

• Formal negotiation processes can slow down changes

• Need for clear communication channels

• Resource allocation between different customers

• Service level agreement management overhead

• Balancing competing customer priorities

• Documentation and support requirements

• Training and onboarding new customer teams

Best Practices

1. Contract Management

   • Clear service level agreements

   • Explicit API contracts

   • Version management strategy

   • Change notification process

2. Service Evolution

   • Planned deprecation cycles

   • Feature roadmap sharing

   • Customer feedback loops

   • Migration assistance

3. Performance Management

   • Regular capacity planning

   • Usage monitoring

   • Performance SLAs

   • Resource allocation

4. Relationship Management

   • Regular check-ins

   • Clear escalation paths

   • Feature request process

   • Customer success metrics

Architect's Alert 🚨

While Customer-Supplier relationships provide clear boundaries and expectations, they require significant investment in relationship management. The formality that makes them stable can also make them rigid. Consider carefully whether the overhead of formal agreements is justified by the stability needs of your context.

Implementation Strategies

1. Contract Design

   • Use interface-first design

   • Implement contract testing

   • Define SLA metrics

   • Create customer onboarding plans

2. Service Management

   • Monitor usage patterns

   • Track customer satisfaction

   • Implement feature flags

   • Provide self-service options

3. Evolution Strategy

   • Plan version lifecycles

   • Create migration tools

   • Maintain compatibility layers

   • Document breaking changes

Conclusion

The Customer-Supplier pattern brings formality and clarity to context relationships but requires careful management of both technical and organisational aspects. Success lies in finding the right balance between service standardisation and customer-specific needs.