Connecting a Legacy System to a New Web App: A Practical Integration Checklist
Most new business apps do not start on a blank slate. They have to talk to an old ERP, an accounting package, a government portal or a third-party service that nobody wants to touch. In product work for enterprises, SMEs and government bodies, weak integration and disconnected departments are among the most common problems we see, so integration deserves its own plan from day one. Before you…
Integrating a new web application with legacy systems can be a complex task, but a practical integration checklist can help ensure a smoother process. When starting a new business app, it's essential to remember that it won't be built from scratch and must interact with existing systems like ERP, accounting packages, or government portals.
To avoid common issues, such as weak integration and disconnected departments, it's crucial to have a plan from the beginning. Before writing any code, map out all the systems and their respective owners. Identify every system the new app needs to read from or write to and determine who has the authority to approve changes for each side.
One system should serve as the source of truth for certain data, while another may handle invoices, and so on. Duplicated masters can lead to many sync bugs, so picking the right integration style for each system is vital. A clean REST API, scheduled file exports, or database views are all viable options. Older systems often only support the latter two methods.
To accommodate future changes, design integrations in their own module, creating an adapter layer between your app and each external system. This way, if you need to replace an older system later, you only need to modify one module rather than the entire codebase.
Anticipate failures by incorporating retries, timeouts, and a queue for writes. This ensures that a slow legacy system won't freeze your UI. Logging every exchange is also essential, as it allows you to quickly resolve any discrepancies between numbers in two systems. Finally, ship your integration safely by including integration tests in your CI/CD pipeline with stubbed versions of each external system. This way, a change on your side cannot silently break the link.
Test the performance of your integration with realistic volumes rather than just ten sample records. Treat credentials as secrets and keep API keys out of your repository. Give each integration the least access it needs and consider providing managers with a dashboard featuring role-based views of sync status. This way, problems can be detected before users report them.
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