OK, I would suggest you re-think the whole container approach and use a regular DO "droplet".
Containers are good for applications that are broken down into microservices. Moodle, for good or ill, is a monolithic application. That means it's best suited to a good old-fashioned application server, which should have enough compute and memory to run a web server (Apache, Nginx, etc) and PHP (preferably as FastCGI).
With some (but not much) effort, you can build an image that contains the requisite software to run stateless application servers. The state can be stored in the database and a key/value store like Redis or memcached.
Containers are basically "no go" for Moodle, as you have found, because containers fail all the time, and you need to have an application that expects constant failure.
Open edX was built with that in mind. It looks like a fun project to work with, if you're a systems engineer. If you're interested in delivering a service to teachers and learners, OTOH, use Moodle, use web servers, use caution.