External exposure of services Around this time, we started to see enterprises exploring exposure of interfaces beyond the  boundary of the organization. There are much more challenging security implications in this  situation, so the idea of a secure gateway in the DMZ was introduced, as shown in Figure 3-2  on page 44. Figure 3-2 Externally exposed services 44  Accelerating Modernization with Agile Integration This gateway had only one job: to securely expose the interfaces on the internet, handling  whatever security model was required, and protecting against other forms of attacks, such as  denial of service, and even payload-based attacks, such as XML threats. It then passed the  request on the enterprise’s network to an integration engine that performed the integration to  the back-end system’s protocols, performed data mapping, and did any composition of  invocations that were required to form the response. This situation encouraged a separation  of duties between exposure (on the gateway) and integration (in the integration run time) so  that each component could focus on what it does best. 