How Do You Automate a Legacy System During an ERP Migration?
An ERP migration doesn’t end the day the new system goes live. Most teams run the old and new systems in parallel for weeks or months to validate data before fully cutting over, and someone still has to keep both fed and reconciled during that window. Deck automates that parallel-run period so it doesn’t fall on staff to manually operate two ERPs at once.
What Does It Take to Automate a Legacy System While Migrating to a New One?
Automating a legacy system during migration means keeping the old system’s workflows running exactly as they did before, while data also flows into the new system for validation, without doubling anyone’s manual workload. Deck is a computer use agent platform that automates workflows by operating any web interface directly, so the target system never has to expose an API for it to work, which matters because most legacy ERPs never had a migration-friendly export built in.
A parallel-run automation typically follows this pattern:
- Keep the legacy workflow running exactly as before: order entry, inventory checks, reporting, all through the legacy ERP’s own interface, with no changes to how staff already work.
- Mirror the same data into the new system by operating the new ERP’s interface, or its API where one exists, in step with each legacy transaction as it happens.
- Reconcile both systems daily, flagging any mismatch between legacy and new records as schema-validated JSON downstream for the migration team to review.
- Continue through the full validation window, not just a single test cycle, since data drift often only shows up after weeks of real transaction volume.
- Cut over the legacy workflow only once reconciliation is clean, with no re-platforming risk taken on faith and no surprise gaps discovered after the legacy system is switched off.
The legacy system runs the same as it always did. What changes is that a person no longer has to manually double-enter data during the transition, and the migration team gets a continuous, dated record of exactly when the two systems started agreeing.
Why Does This Beat Manual Double-Entry or Custom Migration Scripts?
Manual double-entry is the default during most migrations: staff enter every transaction into both systems by hand until cutover, which is slow, error-prone, and gets worse as transaction volume climbs during exactly the period accuracy matters most. It also means the parallel-run window tends to get shortened under pressure, which is precisely when data problems go undetected.
Custom migration scripts can sync data once, but a true parallel-run needs continuous, two-way reconciliation over weeks, and a one-time script isn’t built for that. Maintaining it through a multi-month migration becomes its own project, often owned by whichever engineer happened to write it first.
RPA tools like UiPath or Automation Anywhere can technically automate both systems' interfaces, but they’re brittle against the legacy system’s quirks precisely when the migration team can least afford a broken bot mid-cutover. A recorded bot that breaks halfway through validation forces the team back to manual entry at the worst possible moment.
Deck runs both interfaces continuously and adapts to the legacy system’s behavior the way a person would, so the parallel-run period doesn’t become its own separate maintenance burden layered on top of the migration itself.
How Are Other Teams Already Doing This?
BuildVision faced a version of this same problem from the sales side: showing manufacturers that automation would work inside their legacy systems, before committing months of engineering to build it. Using Deck, BuildVision could demonstrate one working branch of a manufacturer’s system live, proving the rest was possible without writing production code first, then build the full direct integration only after the contract closed. The same logic applies to a parallel-run migration: prove the legacy workflow keeps running correctly before the team commits further engineering effort to the cutover.
FAQs
Does Deck replace the ERP migration itself?
No. Deck automates the legacy system’s workflows and mirrors data into the new system during the parallel-run window; the migration plan and cutover decision stay with the migration team.
Is Deck useful only during migrations, or ongoing too?
Deck is commonly set up for a migration’s parallel-run period specifically, but the same legacy-system automation can continue after cutover for any workflow the new system still doesn’t cover.
Does Deck work if the legacy ERP has no export or API at all?
Yes. Deck operates the legacy system’s own interface directly, the same way a person would, so a missing export or API doesn’t block the parallel-run automation.
How long does it take to set up a parallel-run automation with Deck?
Setup typically takes days once the legacy workflow is mapped, well within a migration’s planning window rather than adding to it.
What happens if the legacy system and the new system disagree during reconciliation?
Mismatches are flagged as structured records for the migration team to review, rather than resolved automatically, since deciding which record is correct is a judgment call the team needs to make.
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