Legacy-to-Real-Time: An Architectural Path for Incremental Event-Driven Modernisation in Resource-Constrained Enterprise Environments

A billing platform that has outlived two modernisation attempts is not evidence that event-driven architecture fails to deliver on its promises. It is evidence that the migration path assumed conditions the organisation never had. This article develops a sequencing framework for incremental, event-driven modernisation built for enterprises that cannot assume green-field flexibility, specialised platform staff, or patient single-allocation funding. Four criteria are proposed for choosing which legacy system to modernise first: data volatility, downstream consumer count, change-data-capture feasibility, and blast-radius containment. A staged modernisation path follows, tying each stage to a funding-justification checkpoint and an explicit rollback provision. Resource-constrained organisations fund transformation incrementally and will not commit capital stage by stage without evidence the previous stage worked. Migration-readiness research shows that existing assessment frameworks evaluate technical readiness while leaving organisational readiness - funding cadence, staffing depth, disruption tolerance - outside their scope (Pamungkas et al., 2024), and systematic mapping of monolith-to-microservices migrations documents anti-patterns in programmes that pass technical gates and fail anyway (Muraca & Pollo-Cattaneo, 2023). Enterprise architecture governance research describes the staged decision processes through which such organisations actually release funds (Hillmann et al., 2024). The article's position is that sequencing discipline, not the streaming platform or architectural pattern chosen, determines whether incremental modernisation reaches production in a resource-constrained enterprise. A migration framework that does not build funding and rollback checkpoints into its technical sequencing is asking such an organisation for a commitment the governance evidence says it will not make