What integration pattern should an Architect suggest for quick validation of street addresses in Salesforce against a legacy system?

The correct choice is to use an Outbound Message with a Callback for quick validation of street addresses in Salesforce against a legacy system. This pattern allows Salesforce to send a message containing the necessary data (in this case, the street addresses) to the legacy system asynchronously.

Using an Outbound Message is beneficial because it is designed to integrate tightly with Salesforce's platform, providing a reliable way to transfer information without blocking other processes. The legacy system can process the incoming message at its convenience, and once the address validation is complete, it can send a response back to Salesforce using a callback endpoint. This approach ensures that the Salesforce instance does not wait for the validation process to complete, helping maintain system performance and responsiveness.

Furthermore, this pattern supports real-time validation scenarios rather than scheduled jobs or batch processing, making it well-suited for quick address validation where immediate feedback is necessary. This is especially relevant in scenarios where user input needs to be validated instantly during data entry processes.

Other options may involve various levels of complexity or delay. For example, Remote Invocation initiated by Middleware can introduce latency since it often requires a roundtrip through an intermediary, which is not optimal for quick validation. The @Future method with an Apex callout might face issues related to the limitation