Our certificate monitoring KeyChest has an initial RESTful API for remote enrolment of new certificates and for checking certificate expiry. Its design supports automation without any initial security/authorization setup.
Amazon is pretty good at providing a cloud platform with all the tools and infrastructure you may possibly need without looking into the small print. CPU credits are an exception.
We checked recent statistics of the KeyChest service. While the overall load is gradually increasing, we also increase the number of checks we perform. It’s now over 500,000 a day since March 26. But we should be fine till a major system upgrade coming soon.