Clarify an interface’s job before replacing it

Before replacing an interface, establish what work it actually carries today. The technical reason can be justified: an old protocol or an implementation that is hard to maintain can support a change. That alone does not establish which business workflows the replacement must preserve.

The visible transfer is only part of the workflow

In a fictional company, a nightly connection transfers new orders from a portal to the ERP. It also waits for clarification when item identifiers are unknown and returns the ERP order number the following day. Replacing only the initial transfer could lose unresolved requests or omit the route that sends the number back.

The example supports our recommendation to capture exceptions and responses too. An old connection can contain useful work even when its technical form should be replaced. It can also carry rules that nobody needs anymore. Decide what to retain or retire by examining the concrete workflow.

Examine meaning before the new form

Microsoft describes translation between systems with different meanings through the Anti-Corruption Layer. Such a boundary can help separate the new connection from the old system model. It does not decide which waiting steps or responses the business still needs.

Check a normal operation, a deferred case and a delayed response. For each, establish which result must be preserved. Not every existing peculiarity needs a technical copy; a deliberately simplified rule can be the better choice when its consequences are clear.

Size the transition around dependencies

The Strangler Fig pattern describes staged replacement of individual functions. This requires suitable handover points and creates temporary extra work. For a small, clearly bounded connection, a single coordinated switch may be simpler.

The replacement can only be assessed in business terms once open operations also have a path. A successful new connection says little about that. We therefore recommend defining the intended work through concrete cases, then deriving the new connection's scope and transition from them.

Sources

• Microsoft Learn: Anti-Corruption Layer pattern

• Microsoft Learn: Strangler Fig pattern