# Connect the system you still need to run.

Legacy system connectivity

Expose controlled interfaces around existing systems so new applications can be introduced in stages.

## A safe boundary around an older system

Illustrative workflow.

- Legacy application: Existing records and business behaviour
- Adapter: Validation, translation and controlled access
- Modern services: A stable contract for new capabilities



## Stop spreading internal database assumptions

### Let every new application query the old database

Schema details become external contracts and changes become harder to control.

### Introduce one supported integration boundary

Translate data in a dedicated adapter, monitor failures and isolate consumers from internal changes.

## Protect the old system behind a supported boundary.

### Interface discovery

Identify supported exports, database access and application interfaces before choosing a connection.

### Adapter boundaries

Contain legacy formats and assumptions within an adapter that exposes a documented contract.

### Safe synchronisation

Plan batching, replay and reconciliation around the existing system’s capacity and ownership rules.

## Connect what works without exposing what is fragile

Use an adapter to protect consumers from inconsistent formats, old authentication or limited availability. Start with the access the system can safely support.

Illustrative scenario, not a customer case study.

An order platform must update its database and publish an integration event reliably.

Write the business change and outbox record in one database transaction. Publish asynchronously and make consumers tolerate duplicate deliveries using a durable event identifier.

Verification: Measure the oldest pending event and verify consumer behaviour under duplicate and delayed delivery.

## What your team receives

Included scope agreed before delivery.

- Adapter contract: Supported operations, data meaning and access limitations.
- Connectivity implementation: Controlled translation, validation and failure isolation.
- Operating notes: Monitoring, transfer timing, recovery and known constraints.

## What if the legacy system has no API?

Evaluate supported exports, scheduled transfers or controlled database access. Document the limitations and avoid unsupported writes that bypass business rules.