Heroku vs Render
I'm familiar with and have been using Heroku since 2011, so for over a decade. Back then it was aimed at ruby-only software stacks and had some issues with performance and stability.
But
development
Dockerize all the things!
What Docker is and what is it not.
Docker is a software provided by Docker Inc - it's a technology providing containers.
It provides additional abstraction layer and automation of OS level virtualization