Public Sector  ·  Technical Architecture

Legacy Transformation &
Architectural Resilience

Delivering the architectural patterns and core enabling concepts required to displace a complex legacy estate while maintaining continuous delivery of new features.

In association with eSynergy
Sector
Public Sector
Capability
star:modernise, star:architecture
Technology
Azure, LikeC4, Apache Pulsar, FortiADC
The Challenge

Navigating a multi-year transformation without stalling delivery.

The organisation was embarking on a significant multi-year legacy system transformation programme. The challenge was not just to build the new, but to do so while the old remained critical.

The transformation needed to enable incremental development of new features while maintaining strict compatibility with external integrations and downstream processes that were not yet scheduled for modernisation.

Without clear architectural patterns for this transitional state, delivery teams risked building inconsistent, tightly-coupled solutions that would increase technical debt and hamper the long-term goals of the programme.

Pain Points

Legacy integration complexity
Maintaining compatibility with rigid legacy systems and downstream processes created significant drag on new feature development.
Duplication of architectural effort
Different delivery teams were independently solving the same transformation patterns, leading to fragmented designs and wasted engineering time.
Inconsistent auth and security
Bridging legacy authentication mechanisms with modern cloud-native patterns was a complex, recurring challenge for every team.
Risk of "Big Bang" failure
Without a clear strategy for incremental displacement, the organisation faced the high risk of a single, large-scale migration event.
The Solution

Core enabling architectural concepts.

Working at the programme level and alongside the platform team, Starlake (in association with eSynergy) delivered the architectural designs and patterns required to unblock delivery teams and ensure a resilient transformation.

Legacy Displacement Patterns

Defined the patterns for incremental migration, allowing new services to coexist with legacy systems through well-defined interfaces and data synchronisation strategies.

Legacy Auth Integration

Designed concepts for integrating legacy authentication providers with modern identity platforms, enabling seamless user journeys across both environments.

Anti-Corruption Layer (ACL)

Implemented ACL patterns to prevent legacy domain models from leaking into new services, ensuring the new architecture remained clean and purpose-built.

Multi-Region Resilience

Architected a multi-region Azure foundation with failover patterns and state synchronisation, ensuring the new platform met the organisation's high availability requirements.

Event-Driven Patterns

Leveraged Apache Pulsar to implement robust, asynchronous communication patterns between services, reducing coupling and enabling real-time data flow.

Architecture with LikeC4

Utilised LikeC4 for architecture-as-code modeling, ensuring designs were living, version-controlled artifacts that could be easily shared and understood by delivery teams.

Outcomes

A blueprint for successful legacy displacement.

By working at the programme level, the benefits of the architectural designs were realised across all delivery teams, creating a unified and confident transformation path.

Accelerated feature development
Delivery teams no longer spent weeks designing integration patterns from scratch, enabling them to focus immediately on delivering new business value.
Reduced duplication of effort
Standardised patterns for ACL, auth integration and messaging meant teams reused proven designs rather than reinventing them.
Architectural resilience by design
Multi-region patterns and robust event-driven designs ensured the new platform was more resilient and scalable than the systems it replaced.
Continuous legacy compatibility
The displacement patterns ensured that legacy systems and downstream processes continued to function without interruption as modernisation progressed.
Unified delivery alignment
Living architecture models in LikeC4 provided a single source of truth that aligned developers, architects and programme leadership.
Work with Starlake

Facing a similar challenge?

We'd be thrilled to hear about it and discuss your needs.