Replace a legacy system
Move off a legacy system, one piece at a time
We reconstruct what your old system really does from the evidence it leaves, run the new version beside it on your real data, and switch over piece by piece, each step with a way back. This offer is on our roadmap.
Roadmap
“Our core system has grown rigid, its platform is reaching its end of life, and only one or two people still understand it.”
How it goes
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Check the fit
Is there a record of what the system did, and someone who knows it? Together we pick the first piece: painful enough to matter, small enough to finish in three months.
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Reconstruct from evidence
AI reads the records and the data the old system left and proposes how that piece works. Every rule it proposes names its source; nothing without evidence is accepted.
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Confirm with your expert
In guided sessions your expert confirms or corrects each rule. What the evidence cannot settle becomes a question for them, and what nobody knows is written down as a known gap.
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Run alongside
The new version receives the same changes as the old one, without any authority yet, and the results are compared. Every difference comes back as a question, through at least one month-end.
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Switch over, piece by piece
First your people read from the new system, then they work in it, while the old one is still fed what it needs. Each step can be turned back, and the old parts are retired one by one.
Why this is safer than a rewrite
Most legacy projects fail in the same place: a new system is built from what people remember, and on the day of the switch it turns out to behave differently from the old one in ways nobody wrote down. The knowledge was in the old system and in one person’s head.
Here the old system is the first source, not the last. What it recorded, its data and its own records of what happened, is read first, and every rule of the new version points back to where it came from. Your expert’s time goes into the questions the evidence cannot answer, instead of into explaining everything from scratch.
Then the new version proves itself on your real data before it is trusted with anything. It runs beside the old system and receives the same changes; where the two disagree, the difference is a question to answer, not a surprise after the switch. Only when they agree through a full business cycle do your people move over, first to read, then to work, and each step can be turned back.
Because every decision in the new system is recorded, we migrated correctly is not a claim but something an auditor can check. And once a piece runs on the new system, it changes like any other part of your software: the features that were impossible in the old system become the next steps.
What you keep
- A description of what your old system really does, with the evidence for every rule, even if you stop after the first steps
- The old system’s vocabulary, written down in your words
- A comparison report from the parallel run that your auditor can check
- Software on an open-source foundation, in your own repository
Frequently asked questions
Is this a big-bang rewrite?
No. Big-bang rewrites are what fails most often. The new system runs beside the old one until the results agree, and the switch happens on the day the least changes.
How long does it take?
Each piece is cut so that it fits into about three months from the first run to switching off the old part. How long the parallel run lasts is set by your business calendar, for example a month-end or a quarter-end, not by us.
When would you advise against it?
When there is no record of what the system did and nobody who knows it, when the system is actually fine, or when moving it unchanged to new hardware is all you need. Then we say so.
Can we start today?
The method is worked out; the tools that bring history across and compare old and new results are still being built. If a migration is coming, talk to us: a technical assessment of your system can start before that.
Not ready to commit? Talk to us first — free.
Book a free 30-minute intro callFree 30-minute intro call — no obligation.
Find out if Reventless fits
A short conversation is enough to see whether your business process and Reventless are a match — no obligation.
Free 30-minute intro call — no obligation.