When I say "Legacy Core," I don't just mean COBOL on a mainframe (though that is the archetype). A legacy core can be a microservice mesh built three years ago if the architecture was wrong. It is defined by three characteristics:
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Every business has one. That one system that nobody wants to touch. The codebase that has no tests, three layers of deprecated frameworks, and a single, terrified contractor in Nebraska who holds the encryption keys in their head. legacy core
For the last decade, the industry mantra has been the : build a new system around the edges, intercept calls, and slowly choke out the old one.
These systems are typically , meaning all functions are tightly coupled into a single, massive piece of software. Most were built on mainframe technology in the 1970s and 1980s, designed for stability and batch processing rather than the real-time, 24/7 demands of modern mobile banking. The True Cost of "Inertia" When I say "Legacy Core," I don't just
Stop trying to kill the core. Contain it.
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Finance loves the legacy core because it is predictable. Operations loves it because they know the failure modes. Product hates it because they can’t ship.