Does anyone have experience in hosting the contact form (thank you.php) using AWS Lambda with custom runtime? Introducing the new Serverless LAMP stack | AWS Compute Blog
Hi @viraf, welcome onboard! 
No experience with AWS, but I did have a read of your link.
Knowing website builds for the most part are simple in nature and that goes for the hosting as well, I feel the AWS LAMP is overkill for a Sparkle website.
We host our clients on a native Linux-based (with cPanel) hosting platform running the most up to date PHP and have never had any issues with the “thankyou.php” page.
If you configure Sparkle to send email to a custom SMTP server, there is no local email delivery so the lambda just needs to be a very simple PHP environment.
Setting up that is all about configuring the lambda in a way that mimics a standalone server, with relation to the very little amount of PHP code in the Sparkle thank you page, so I would imagine the default for a PHP-running lambda would work or be very close.
However I don’t have experience or knowledge of how that’s done, so can’t really help you there.