When creating the web infrastructure for our start-up, I wanted to host our app on a PaaS to get started quickly.
A very popular one for Rails is Heroku, which I love for free hobby side projects, but never used professionally. On the other hand, I was very familiar with the AWS ecosystem, and since I was going to use some of its services anyways, I thought: why not go all in on it?
It turns out that Amazon offers a PaaS called AWS Elastic Beanstalk, which is basically like an “AWS Heroku”. It even comes with a similar command-line utility, called "eb”. While edge-case Rails problems are not as well documented as with Heroku, it was very satisfying to manage all our cloud services under the same AWS account. There are auto-scaling options for web and worker instances, which is a nice touch. Overall, it was reliable, and I would recommend it to anyone planning on heavily using AWS.
I'd go with Kubernetes and Knative or similar. There you have buildpacks like heroku without having the heavy vendor lock you would have with amazon. By doing so you could still move to on premise installation without doing much.