Integration, Interoperability, and Legacy System Connectivity
What this domain tests
Integration patterns, APIs, events, oracles, interoperability, and legacy connectivity. Expect questions on finality, idempotency, and cross-chain risk.
Core rules
- Integrate through narrow, authenticated APIs. Fabric Gateway, Corda RPC, and EVM JSON-RPC are common entry points.
- Design for asynchronous confirmation: a submitted transaction is not committed until finality. Use idempotency keys, retries with backoff, and an outbox pattern to avoid duplicate postings.
- Events notify downstream systems, but they are not a guaranteed message bus. Pair events with reconciliation.
- Oracles bring external data on-chain and create a trust boundary. Prefer multiple signed sources and on-chain validation.
- Interoperability options include shared standards, relays, bridges, sidechains, atomic swaps, and message formats such as ISO 20022 or HL7. Bridges concentrate risk.
Worked example
An ERP creates a purchase order and calls chaincode to record it. The API times out. A naive retry creates a duplicate order. The correct design uses the ERP order ID as an idempotency key checked by chaincode, then waits for a commit event before updating ERP status. Reconciliation compares on-chain state to ERP state nightly. The reasoning: distributed systems fail ambiguously; the integration must make retries safe.
Traps
Do not assume a 200 response means final settlement. Do not put every master-data field on-chain. Do not trust a single oracle. Do not treat a bridge as trustless by default.