# 4.1	Extend the reach for existing applications / legacy applications

## Business use case narrative

![4.1-Extend-the-reach-for-existing-or-legacy-applications](images/4.1-Extend-the-reach-for-existing-or-legacy-applications.png)

The gateway enterprise integration pattern can be used to expose existing legacy applications as standardized services 
such as REST APIs or SOAP services by hiding the complexity introduced by existing service. 

By adhering to this pattern, using ESB, users can extend the reach to existing service over popular standard protocols.

## Sub-Scenarios

- [4.1.1 Expose back-end(s) exposed over HTTP as SOAP service](4.1.1-Expose-back-ends-exposed-over-HTTP-as-SOAP-service)
- [4.1.2 Expose back-end(s) exposed over HTTP as REST API](4.1.2-Expose-back-ends-exposed-over-HTTP-as-REST-API)
- [4.1.3 Expose file-based systems over HTTP/S](4.1.3-Expose-file-based-systems-over-HTTP)
- [4.1.4 Expose back-end services based on proprietary protocols over standard protocols](4.1.4-Expose-back-end-services-based-on-proprietary-protocols-over-standard-protocols)

