What does HackerNews think of dockersh?
A shell which places users into individual docker containers
Language:
Go
The feature is more similar to e.g. dockersh than just exec https://github.com/Yelp/dockersh
Or e.g. change ssh config to use ForceCommand.
That said, the main benefit is not just that a shell gets a container but that you can easily compose this feature with the container / image ecosystem to deploy specialized shells. Perhaps even you don’t need a VM to service the request but rather a container orchestrator ..
Hosted https://github.com/Yelp/dockersh might fit your requirements to a degree.
Yelp built something you can run on a server that will do that with Docker containers (https://github.com/Yelp/dockersh) but for you to not pay for it during the downtime, you'd need someone else to provide this as a service to you.