We are running mapserver in production in the cloud (AWS lambda) to visualize lots of different data using WMS. We're also doing lots of processing using GDAL in the cloud as well. Compared to ESRI it's amazingly cost effective even considering Amazon's high prices.

nice. If you aren't already familiar, you might be interested in this platform for Dutch geospatial data: https://github.com/PDOK . They use mapserver on the cloud at massive scale, and all of their infra is open.