Zero-Downtime Modernization of Financial Clearing Engines: A Systematic Review

Abstract

Financial clearing engines underpin global payment networks, securities settlement platforms, and interbank transaction infrastructures, processing trillions of dollars in financial transactions every day. Despite their critical role, many clearing systems continue to operate on legacy monolithic architectures that are difficult to scale, maintain, and modernize without disrupting essential services. This study presents a systematic literature review of 48 primary research studies published between 2015 and 2026, focusing on architectural approaches that enable zero-downtime modernization while preserving transactional integrity, deterministic ordering, and regulatory compliance. The review identifies five interdependent modernization capabilities that consistently emerge across literature: Strangler Fig decomposition, deterministic append-only execution, micro-batch stream processing, active–active replication, and continuous reconciliation. Together, these patterns support incremental migration from legacy systems to cloud-native architectures without compromising settlement accuracy or operational continuity. Building on the synthesized evidence, the study proposes the Verifiable Migration Mesh (VMM), a control-plane framework that integrates observability, validation, risk assessment, and execution governance throughout the modernization lifecycle. The findings indicate that organizations adopting these architectural strategies can achieve availability levels approaching 99.999%, divergence rates below 0.02%, and throughput improvements ranging from 3.8× to 6× compared with traditional clearing infrastructures. The review also highlights unresolved challenges, including regulatory acceptance of event-sourced ledgers, formal verification across heterogeneous distributed environments, and organizational readiness for large-scale transformation. By consolidating fragmented research across software architecture, distributed systems, and financial technology, this study provides a comprehensive roadmap for advancing zero-downtime modernization as a mature and dependable engineering practice for future financial infrastructures.