9. Architecture Decisions

9.1 Decision Record Format

This section documents significant architectural decisions using the Architecture Decision Record (ADR) format. Each decision includes context, considered options, and rationale.

9.2 Architecture Decision Records

Infrastructure & Platform Decisions

• ADR-001: Microservices Architecture
  Adopting microservices with domain-driven service boundaries for scalability and team autonomy.

• ADR-003: .NET Aspire for Cloud-Native Development
  Using .NET Aspire as the primary cloud-native development framework for simplified orchestration.

• ADR-007: Container-First Deployment Strategy
  Container-based deployment using Docker and Azure Container Apps for consistency and scalability.

• ADR-008: API Gateway Pattern Implementation
  YARP-based API Gateway for unified client entry point and cross-cutting concerns.

Data & Persistence Decisions

• ADR-004: PostgreSQL as Primary Database
  PostgreSQL as the primary database for ACID compliance, JSON support, and performance.

• ADR-002: Event-Driven Architecture with CQRS
  Event-driven architecture with CQRS for scalability and loose coupling between services.

Security & Identity Decisions

• ADR-005: Keycloak for Identity Management
  Keycloak for centralized identity and access management with standard protocols.

Communication & Real-time Decisions

• ADR-006: SignalR for Real-time Communication
  ASP.NET Core SignalR for real-time bidirectional communication in chat features.

AI & Intelligence Decisions

• ADR-009: AI Integration Strategy
  External AI services integration through abstracted interfaces for search and chat capabilities.

9.3 Decision Timeline

The following timeline shows when major architectural decisions were made:

9.4 Decision Impact Matrix

The following matrix shows how architectural decisions influence different quality attributes:

Decision	Performance	Scalability	Security	Maintainability	Testability
Microservices	⚠️ Network overhead	✅ Independent scaling	✅ Fault isolation	⚠️ Complexity	⚠️ Integration testing
Event-Driven CQRS	✅ Read optimization	✅ Separate workloads	✅ Audit trail	⚠️ Eventual consistency	⚠️ Event testing
PostgreSQL	✅ Query performance	⚠️ Vertical scaling	✅ ACID compliance	✅ Mature tooling	✅ Local testing
Keycloak	⚠️ Token validation	✅ Horizontal scaling	✅ Standard protocols	✅ Centralized mgmt	✅ Mock integration
SignalR	✅ Real-time updates	✅ Azure scaling	✅ Integrated auth	✅ .NET native	⚠️ Connection testing
API Gateway	⚠️ Single bottleneck	✅ Load balancing	✅ Centralized auth	✅ Cross-cutting	✅ Integration point
Containers	✅ Resource efficiency	✅ Horizontal scaling	✅ Isolation	✅ Consistency	✅ Environment parity

Legend: ✅ Positive impact, ⚠️ Requires attention, ❌ Negative impact

9.5 Decision Dependencies

The following diagram shows how architectural decisions depend on each other:

9.6 Change Management

Adding New ADRs

When proposing new architectural decisions:

1. Create ADR File: Use the next sequential number in the adr/ directory
2. Follow Template: Maintain consistent format across all ADRs
3. Update Index: Add reference to this main file and ADR README
4. Review Process: Get stakeholder review before marking as "Accepted"
5. Link Relations: Reference related ADRs and update dependency diagrams

Modifying Existing ADRs

When existing decisions need updates:

1. Status Change: Update status (Deprecated, Superseded, etc.)
2. New ADR: Create new ADR that supersedes the old one
3. Cross-Reference: Link between old and new decisions
4. Impact Analysis: Document impact on dependent decisions

ADR Template

# ADR-XXX: [Decision Title]

## Status

**[Proposed|Accepted|Deprecated|Superseded]** - [Date]

## Context

[Describe the situation and constraints]

## Decision

[What was decided and key implementation details]

## Rationale

[Why this decision was made]

## Consequences

### Positive

[Benefits and positive outcomes]

### Negative

[Drawbacks and risks]

## Alternatives Considered

[Other options that were evaluated]

## Related Decisions

[Links to other relevant ADRs]

9.7 Future Considerations

Pending Decisions

The following architectural decisions are under consideration:

• Service Mesh: Evaluating Istio or Linkerd for advanced traffic management
• Event Sourcing: Full event sourcing for critical business aggregates
• Multi-Region: Cross-region deployment strategy for global availability
• Advanced AI: Integration of larger language models and specialized AI services

Review Schedule

Architectural decisions should be reviewed periodically:

• Quarterly Reviews: Assess current decisions and identify needed changes
• Technology Updates: Evaluate impact of new .NET and Azure features
• Performance Reviews: Review decisions based on production metrics
• Team Feedback: Incorporate development team experiences and suggestions