Moving inventory functions off SAP MM feels all-or-nothing, and that is exactly why most attempts stall: a big-bang cutover of something as central as materials management is too risky to approve. The strangler-fig pattern is the way out. You grow a new system around the old one, route functions to it one at a time, and retire SAP MM piece by piece, never betting the operation on a single switch.
The pattern, applied to inventory
The strangler fig (named for the vine that grows around a tree and gradually replaces it) means:
- Put a facade in front of MM. Route inventory reads/writes through an interface layer rather than letting consumers call SAP directly. Initially the facade just forwards to MM.
- Carve out one capability. Pick a bounded, lower-risk function, say goods-receipt posting or a specific stock query, and implement it in the new system.
- Redirect that function through the facade to the new implementation, while everything else still hits MM. Run them in parallel, compare outputs, and verify before trusting it.
- Repeat, moving capabilities one at a time, until MM is doing little, then nothing.
- Retire MM for inventory once the last function has moved and been verified.
Why this beats a big-bang
- Risk is bounded per step. If a migrated function misbehaves, you roll back one capability, not the whole system.
- Value lands early. The first migrated function delivers benefit before the program finishes.
- Verification is continuous. Running new and old in parallel and reconciling (the accuracy discipline again) catches divergence while MM is still the source of truth.
The hard parts to plan for
- Data ownership and sync. While both systems run, one must own each stock figure. Dual-write or event-stream the changes, and decide the system of record per capability, not globally.
- The facade is load-bearing. It is the seam the whole migration hangs on; design it to express inventory operations cleanly, not just to proxy SAP calls.
- Consistency under concurrency. Stock decrements must stay correct across the seam, the same available-to-promise concern, now spanning two systems.
The takeaway
You do not have to choose between living on SAP MM forever and a terrifying big-bang rewrite. Put a facade in front of it, migrate inventory capabilities one verified step at a time, and let the new system gradually strangle the old. It is slower than a rewrite on paper and far safer in practice, which for a system this central is the trade worth making.
Working through this in your warehouse?
The team that wrote this also implements inventory architecture, audits operations, and advises on transformation engagements. AvanSaber’s inventory practice runs case-by-case engagements for mid-market and enterprise inventory teams.
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