“We'll just hook it up to the ERP” is a sentence that makes any experienced project manager sit up. Integrations are the most underestimated part of enterprise development: 20 % of the budget and 60 % of the problems.
The five classic mistakes
1. Nobody looked at data quality — and the ERP holds thirty thousand duplicate customers. 2. A “once a night” sync for a process that needs data now. 3. No outage scenario: the ERP goes down for maintenance and orders fall into a black hole. 4. An integration without an owner — a code list changes and for three months nobody knows why prices do not match. 5. Point-to-point spaghetti: the fifth system connected to the previous four means twenty interfaces to maintain.
How to do it properly
An integration layer (API gateway or middleware) instead of spaghetti, a message queue for outage resilience, monitoring with alerts, and a contractually named owner for every interface. Sounds more expensive — until you price your first weekend invoicing outage.
Our price calculator charges +8 % per integration. Now you know what is inside those percent: not optimism, but twenty years of other people's mistakes.