Jeff Barr, on the AWS News Blog:
Powered by Mac mini hardware and the AWS Nitro System, you can use Amazon EC2 Mac instances to build, test, package, and sign Xcode applications for the Apple platform including macOS, iOS, iPadOS, tvOS, watchOS, and Safari. The instances feature an 8th generation, 6-core Intel Core i7 (Coffee Lake) processor running at 3.2 GHz, with Turbo Boost up to 4.6 GHz. There’s 32 GiB of memory and access to other AWS services including Amazon Elastic Block Store (EBS), Amazon FSx for Windows File Server, Amazon Simple Storage Service (S3), AWS Systems Manager, and so forth.
Mac instances run macOS 10.14 (Mojave) and 10.15 (Catalina) and can be accessed via command line (SSH) or remote desktop (VNC). The AMIs (Amazon Machine Images) for EC2 Mac instances are EC2-optimized and include the AWS goodies that you would find on other AWS AMIs: An ENA driver, the AWS Command Line Interface (CLI), the CloudWatch Agent, CloudFormation Helper Scripts, support for AWS Systems Manager, and the ec2-user account. You can use these AMIs as-is, or you can install your own packages and create custom AMIs (the homebrew-aws repo contains the additional packages and documentation on how to do this).
The plan on rolling out M1 Mac minis early next year, and while this is neat, I still think what MacStadium offers is a lot more compelling if you need a Mac in the cloud all the time.