Indeed it’s 2020 and yet to see any major open source work from Amazon (which has benefited a lot from open source itself using Perl, CPAN, C, Java, Linux etc.). In this respect IBM, google, Microsoft, Facebook and Apple are far better. Here even Oracle fare better due to acuisition of MySQL and sun microsystems.
I believe the major contribution from amazon might be hiring some of the open source developers to build proprietary systems. Those developers in spare time or weekends continue their open source project, but I do not have any study or articles on it.
Based on my information in 2013, amazon built their cloud using Xen hypervisor and related tools and libraries. Libvirt is one of the key libraries providing beautiful abstractions and language bindings to manage xen on Linux node at that time.
It will be nice if you can point to code from Amazon on low level library like Libvirt for cloud computing.