When a leading Belgian public enterprise approached us with the need to modernize its brittle, point-to-point BizTalk integration setup, we knew the mission would go far beyond technology. It would touch architecture, governance, operations, people and strategy — all without disrupting day-to-day business.

The legacy landscape comprised over 130+ mostly undocumented functional flows, many of which had grown organically over the years. The main IT systems were Salesforce, SAP, an impressive GIS software and many other legacy and custom applications. It was a textbook case of tight coupling: fragile, opaque, and expensive to change. The consequences were clear: recurring incidents, long lead times, and operational inefficiencies that left both business and IT teams frustrated.

Step 1 — Diagnosing the Landscape

Our priority was to map the existing integrations and identify both technical pain points and functional bottlenecks. We worked closely with operational teams and business stakeholders to extract:

• Recurrent incident patterns

• Redundant data flows

• Painful maintenance routines

• Security issues and potential attack vectors

• Flows complexity and system coupling

• Existing frictions in the development and delivery process

At the same time, we defined the platform selection criteria, aligned with functional and non-functional requirements such as security, scalability, maintainability, and hybrid deployment capability — all crucial for the company’s regulatory and operational context.

Step 2 — Designing the Target Architecture

• We advocated for an API-led architecture for its modularity, reusability and capacity to isolate impacts of changes and evolutions in the IT landscape (modernization of legacy, migration to SAP S/4HANA,…)

• Event driven asynchronous messaging for reliability and guaranteed delivery.

• Leveraging the MuleSoft Anypoint Platform, as it met all our criteria’s for the selection of a proven, robust hybrid iPaaS capable of running the most demanding use cases.

To validate our assumptions on API Led granularity and reuse potential, we modeled the future-state integration layer using ArchiMate.  

This gave us:

• A common language with the enterprise architects

• A complete cartography of all APIs composing the future API landscape in Enterprise Architect (Sparx Systems)

• Early visibility on reusability potential and common integration patterns

• A tangible estimation on time and costs for the whole migration effort

This model became a strategic asset, guiding platform setup, security policies, flow orchestrations and governance decisions across the board.

Step 3 — Incremental Migration with Zero Downtime

We helped in refactoring the whole legacy integration, flow by flow, in well-defined System, Process, and Experience APIs following our new governance and integration patterns.

The migration was structured in waves. For each functional domain:

• We co-designed and validated the API contracts and API Led composition with business and technical stakeholders

• Pushed for improvements in business value in the new flow design wherever possible

• Improved the delivery process with API first approach and DevOps practice (SDLC)

• Ensured no disruption to ongoing business operations

By embedding ourselves in the customer’s delivery organization and securing C-level sponsorship, we maintained strong alignment throughout the program. The collaboration extended from backlog grooming to deployment readiness checks.

Results That Speak for Themselves

API reuse KPI: We had initially targeted for 30% reusability of APIs across functional flows. By the final migration wave, we were consistently achieving over 50% reuse, significantly reducing development time and improving consistency.

Time-to-market KPI: delivery time from code to deployment for a functional flow went well beyond expectations, from 50 md(!) down to 10 md per flow, including end to end testing and documentation.  
But more importantly, no major incidents occurred during the migration, despite the complexity of moving away from a legacy system.

Today — Trusted Strategic Advisor

Our collaboration didn’t end with the migration. We continue to advise the client on:

• Their API governance model

• DevOps and CI/CD maturity for integration delivery

• The strategic alignment of their integration layer with their digital transformation roadmap

This transformation journey highlights what’s possible when architectural rigor, platform strategy, and close collaboration come together. For organizations burdened with legacy integration, the shift to API-led design is more than a technical upgrade — it’s a foundational step toward agility and digital resilience.

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