Why legacy integration is the hardest part of cloud migration
Lift-and-shift gets the headlines, but the systems you cannot move are what make or break a migration. How we approach the 20-year-old ERP nobody wants to touch.
Every cloud migration deck has the same slide: boxes labeled “on-prem” on the left, a confident arrow, and boxes labeled “cloud” on the right. What the slide never shows is the box that can’t move — the twenty-year-old ERP that runs invoicing, the industry-specific application whose vendor disappeared in 2014, the database that four other systems quietly depend on.
In our experience, that box is where migrations succeed or fail.
The systems you can’t move are the ones that matter
There’s a reason that old system is still running: it works, the business depends on it, and replacing it is a seven-figure project with a multi-year payback nobody wants to sign off on. Telling a client to “just modernize it” is consultant-speak for “your problem, not mine.”
The honest answer is that most businesses will run mixed-generation infrastructure for years — and that’s fine, if the generations can talk to each other.
What integration actually looks like
When we take on a migration with legacy anchors, the work breaks down into three parts:
1. Map the real dependencies. Not the ones in the documentation — the real ones. We trace what actually reads from and writes to the legacy system: scheduled jobs, shared folders, that Excel macro in accounting. Every migration horror story starts with a dependency nobody knew existed.
2. Put a modern interface in front of old systems. The legacy system doesn’t need to change; it needs a translator. An API layer or data pipeline in front of it means everything new — cloud apps, dashboards, AI assistants — integrates with the interface, not with the 20-year-old internals. When you eventually do replace the system, you swap what’s behind the interface and nothing downstream notices.
3. Move in phases, and keep a way back. Big-bang cutovers are how you end up in the news. We migrate workload by workload, run old and new in parallel where it matters, and keep rollback paths open until the new environment has earned trust.
The payoff nobody mentions
Here’s the part that gets missed: once a legacy system has a clean interface in front of it, it stops being a blocker for everything else. Want AI-powered search over customer history that lives in the old database? Possible now. Automated reporting that used to require a manual export? Possible now.
Integration isn’t the boring prerequisite to modernization. It is modernization — done in an order that doesn’t bet the company.
Cloud Square connects past, present, and future technology into one working system. If you have a “box that can’t move,” we’d like to hear about it.