List systems and data owners
Specify the sending application, receiving application, records exchanged and business outcome. Agree which system owns each field. Include authentication constraints, rate limits, vendor support expectations and the business owner who can resolve conflicting records.
Define failures before the happy path
A request may time out after the receiving system has already committed a change. Plan idempotency keys, retry windows, dead-letter handling and alerts. Decide which operations can safely repeat and which require manual review to prevent duplicate orders, invoices or notifications.
Secure the boundaries
Use narrowly scoped credentials and rotate them using an agreed process. Avoid sending unnecessary personal data. Protect webhook endpoints, validate incoming signatures when available and log failures without storing secrets in plaintext. Treat compliance requirements as design inputs rather than late-stage patches.
Create a reconciliation plan
Monitor both technical errors and business mismatches. Build a dashboard or scheduled report that highlights records stuck between systems. Test vendor downtime and schema changes before go-live. Operational ownership is what keeps an integration dependable six months after the launch.
Agree on a data contract with real examples
Document each field’s meaning, source system, valid values, validation rules, privacy classification and accepted delay. Specify whether updates are full replacements, partial patches or immutable events. Do not assume two systems mean the same thing by terms such as customer, order, paid or active. Use realistic edge cases in your contract tests, including missing identifiers, duplicate records and a customer who changes their details while another system is offline.
- Authoritative source for each object and field
- Versioned schema and sample error responses
- Expected update order and latency
- Who owns reconciliation disputes
Make repeated delivery safe
External APIs and webhooks can time out after successfully processing a request; a retry may otherwise create duplicate records or charges. Where supported, design idempotent operations or unique event keys and durable deduplication. Use bounded retries with backoff for transient errors, not infinite loops. Give permanent validation errors a review queue and an explanation. A circuit breaker can protect overloaded dependencies, but it cannot replace business-level reconciliation.
Test rollback and operational ownership
Simulate unauthorized tokens, rate limits, removed API fields, partial outages and out-of-order notifications. Ensure logs contain correlation identifiers while masking secrets and personal data. Decide how operations staff will find stuck records and replay them safely. Write a rollback or feature-disable plan before the integration processes business-critical transactions. An integration is complete only when a team knows how to diagnose and recover it.