Architecture decisions
Short answers grounded in enterprise work, not generic tutorials.
IO fits when you need deep block customization, custom checkout and a mature apps ecosystem. FastStore when the storefront needs headless performance, frontend control and a modern GraphQL BFF. The real trade-off is usually time-to-market vs experience control and future debt.
If the domain is intrinsically commerce (promos, checkout UX, storefront) and benefits from VTEX identity, an app makes sense. If it's core business logic, heavy ETL or a system that already lives outside, externalize and integrate. Putting everything inside turns the platform into a hard-to-operate monolith.
Decouple with queues or events, idempotency, backoff retries and a visible reconciliation state. The storefront shouldn't wait on the ERP on the critical purchase path unless business requires it. In that case you need explicit degradation design.
First map whether Checkout UI Custom, apps, orderForm or a pre/post-checkout flow can solve it. If nothing works without breaking upgrades, the trade-off is: simplify the business requirement, or accept high maintenance cost with clear ownership and regression tests.
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