Hi Satendra,
Without knowing more about your integration project, it's a little difficult to answer in more detail but i'll try to distinguish the 2 products and hopefully that should give some insight.
The AWS API Gateway is a managed service offering by AWS used for creating, securing, maintaining and publishing your APIs (with a bit of monitoring thrown in for good measure). It provides a lot of the features you'd expect in a gateway i.e request throttling, security etc while integrating closely with other AWS services (for example AWS Gateway uses CloudWatch to monitor your APIs, and allows you to set up custom alarms).
ACE (Formally IIB) is an integration platform and ESB that provides extended connectivity across multiple applications and disparate formats and protocols. While it provides the ability to create and expose APIs (with closer integration to IBM API-Connect than AWS API Gateway), it is designed for the more complex integration patterns and will probably sit in a different place in your estate than a Gateway would.
Hope this helps, if you'd like any more information please feel free to get in touch!
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Connor Smith
Middleware Integration Consultant
Lightwell
+447500965974
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