2  Executive Summary & Objectives

2.1 Project Overview

Hub is a legacy client-server platform built with an Angular front end and a C# back end that has grown into a tightly coupled monolith over time. The current architecture has become increasingly expensive and risky to modify, slowing delivery and increasing operational burden.

This initiative introduces a decoupled integration model that enables staged migration away from the current platform while preserving business continuity. The target approach combines:

  • Event publication to notify downstream systems that business changes have occurred.
  • Consumer-driven data retrieval (via GraphQL) so consumers can request only the data they need.
  • RESTful APIs for controlled create, update, and delete operations back into Hub using existing business rules.

The strategic outcome is a transition architecture that allows the current and future systems to run in parallel, remain synchronized, and evolve independently.

2.2 Business Goals & Technical Objectives

The modernisation effort is designed to achieve the following outcomes.

2.2.1 1. Reduce Cost and Change Friction

  • Lower the effort required to deliver enhancements by reducing direct coupling between publisher and consumer implementations.
  • Decrease maintenance overhead caused by monolithic release coordination and schema-heavy integrations.
  • Enable smaller, safer increments of change instead of broad platform-wide deployments.

2.2.2 2. Improve Scalability and Integration Flexibility

  • Support additional consumers without requiring each one to adopt a rigid, centrally versioned payload model.
  • Allow each consuming system to retrieve fit-for-purpose data projections through GraphQL.
  • Maintain compatibility across tenant boundaries where direct shared bus management is difficult.

2.2.3 3. Protect Business Continuity During Migration

  • Keep legacy and target solutions operational during transition.
  • Preserve data consistency between current and new platforms through event-driven synchronization patterns.
  • Minimize downtime and business disruption while progressively moving capabilities to the new platform.

2.2.4 4. Strengthen Security and Platform Readiness

  • Evolve existing REST interfaces toward modern authentication and authorization patterns.
  • Retain existing domain validation and business rules in Hub during the transition phase.
  • Establish a secure, auditable integration boundary that supports long-term platform governance.

2.3 Scope and Boundaries

2.3.1 In Scope

  • Definition of the event + REST integration model for staged decoupling.
  • Introduction of consumer pull patterns for downstream data consumption.
  • Modernisation of API security controls required for non-UI integration consumers.
  • Transitional coexistence model covering synchronization, operability, and rollout.

2.3.2 Out of Scope (This Phase)

  • Full replacement of all Hub internal domain logic.
  • Immediate decomposition of all monolithic components.
  • One-step migration of all consuming systems.

2.4 Success Metrics and KPI Targets

Success will be measured with explicit technical and operational indicators.

2.4.1 Delivery and Change Efficiency

  • Reduced lead time for integration changes compared to the current baseline.
  • Fewer cross-team release dependencies required for downstream consumer updates.
  • Increased deployment frequency for integration-related changes without instability.

2.4.2 Reliability and Data Integrity

  • No critical data loss incidents during synchronization between legacy and target systems.
  • Defined SLO attainment for event propagation and REST processing.
  • Measurable reduction in synchronization defects and manual reconciliation effort.

2.4.3 Operational Stability

  • High availability maintained for existing business-critical workflows during migration.
  • Controlled rollback pathways demonstrated for key transition milestones.
  • Reduction in production incidents attributable to integration coupling.

2.4.4 Security and Compliance

  • Adoption of modern authentication mechanisms on integration-facing APIs.
  • Auditability of integration operations and traceability of change events.
  • Zero unresolved high-severity security findings for the decoupled integration surface at go-live.

2.5 Definition of Success

This initiative is successful when Hub can continue serving business operations while new capabilities are delivered through a decoupled model, consumers can independently access required data, and the organisation can migrate incrementally with lower risk, lower change cost, and stronger operational control.