Investigating Docker

I use multiple docker containers and Kubernetes on AWS.

Not sure what your concerns are, you just need to make sure you map and plan your application correctly. For one, i'd definitely not be using file based sessions on docker. I'd a database/redis/dynamodb based session store. Otherwise, Docker is great for deployments and unit testing.

Codeigniter is simply one of the tools you need to learn to be a successful developer. Always add more tools to your coding arsenal!