If a legacy system still runs revenue, replacing it is optional. Connecting it safely is not. Modern tools cannot deliver clean reporting or reliable automation when a core system is isolated.

The goal is to move data and decisions through the business with less manual work and fewer errors, without triggering a risky rewrite.

Choose an integration goal you can measure

Start with one business outcome: faster billing, fewer duplicate records, a cleaner sales pipeline, or better inventory visibility. That goal determines whether you need real-time data or if scheduled updates are enough.

Common ways to connect legacy systems

An API (application programming interface) is a controlled way for software to request data or perform an action. When a legacy tool does not have one, you create a safe interface around it instead of letting every team build one-off workarounds.

• API wrapper: expose a stable API while the legacy system stays unchanged.
• File exchange: scheduled imports/exports (CSV, XML) when real-time is not required.
• Database access: read from replicas or approved views; avoid direct production writes.
• RPA bridge: automate on-screen steps when there is no safe programmatic access and the process is stable.
• Event updates: publish change events so downstream systems stay in sync.

Protect performance and security

Integration can overload older software if every new tool calls it constantly. Use caching, rate limits, and queues. A queue is a holding area that processes requests in order instead of all at once.

Control permissions and log activity. Integration users should have only the minimum access needed for the workflow.

Prevent data drift

Decide where each key record is mastered: customer, invoice, inventory, contract, pricing. If two systems both “own” the same field, they will eventually disagree and staff will start fixing issues manually.

Decisions to make before you build

• Which system is the source of truth for each critical field.
• Whether you need real-time sync or scheduled sync, based on business impact.
• How you detect and handle duplicates, conflicts, and failed updates.
• What monitoring exists: error alerts, performance metrics, and an audit trail.