I am looking to assign a static IP to my Lambda which is being invoked via the API gateway. This is required because, the downstream system that i invoke from this lambda accept
I agree with the answer by John for having static IP whitelisting part. However, it won't resolve your cold start problem because lambda,if ideal, actually takes a small time to start. So I would recommend you also create a Cloudwatch event to hit lambda periodically to resolve this or write a simple code(either in lambda or somewhere else) which sends an empty request periodically so that cold start problem is resolved. You can view the improvement in X-Ray. This is an overhead but one time process.