Moving an integration platform off Informatica, without switching it off.

The situation

Mastercard ran its integration on Informatica PowerCenter — a platform that had done the job for years and had accumulated the history to prove it. The decision to move to SSIS was made above the engineering layer; the question that reached us was how to do it without interrupting anything.

That constraint shapes everything. A platform that processes financial data does not get a weekend of downtime for a rewrite, and it does not get a period where the numbers are allowed to be approximately right.

What we did first

Before rebuilding anything, we inventoried what actually ran: every mapping, every session, every dependency between them, and — the part that takes longest — the transformations whose logic existed only inside the tool.

This is the step that decides whether a migration works. A flow can be reproduced quickly if you know what it is supposed to do. The expensive discovery is always the flow that has been quietly compensating for something else since 2014.

Rebuilding on SSIS

The packages were engineered rather than translated. A mechanical port of PowerCenter mappings into SSIS produces something that runs and nobody can maintain — it carries the shape of the old tool into the new one, along with every workaround.

Where the original logic was sound it was preserved exactly. Where it existed only to work around a PowerCenter limitation, it was removed, and the removal was documented so that nobody would later mistake it for an omission.

Running both, then switching

The two platforms ran in parallel against the same sources, and the outputs were compared. Not sampled — compared. A migration is finished when the new system has produced the same answers as the old one for long enough that the comparison stops being interesting.

Only then did flows move across, in groups, with the old platform still available behind them.