Short answerA legacy system can be connected to modern software, in order of preference, through: an existing API, an API layer built on its database, scheduled file exports, message queues or, as a last resort, controlled screen automation. The usual strategy is to wrap the legacy system behind a stable interface first and then replace its parts one by one, without stopping the business.
Why legacy systems are so hard to replace
An old ERP or in-house program usually holds years of data and business rules nobody fully remembers. It works, more or less. Replacing it in one go is risky and expensive. Connecting it to modern tools is usually the best first step.
Integration options, from best to last resort
An existing API
Some old systems have an API, even if it's SOAP or poorly documented. If it exists, use it: it respects the system's own rules.
An API layer on the database
If the system keeps its data in an accessible database, a small service can expose it through a clean, modern API. Reading is usually safe. Writing must respect the logic the old application applies, so it needs careful analysis.
File exports
Many systems can export CSV, XML or EDI on a schedule. Not real time, but reliable and low risk.
Message queues and events
If the legacy system can send or receive messages, a queue decouples it from modern applications and absorbs its outages.
Screen automation
Robotic process automation drives the interface as a person would. It works when there's no other option, but it's fragile, so it's best used temporarily while something sturdier is prepared.
Wrap first, then replace
Put the legacy system behind a stable interface that modern applications use. Once everything talks to that interface and no longer to the old system, you can replace the parts behind it one by one. This lets you modernise without a risky big-bang migration.
Before you start
- Check what the vendor allows: some licences restrict direct database access.
- Decide which system owns each piece of data: customers, products, orders.
- Expect the old system to be slow or go down: queues, retries and well-handled errors.
- Document what you learn. That knowledge about the old system is valuable.
Published: · Digrow Technologies