Scraping with Selenium in Docker is pretty great, especially because you can use the Docker API itself to spin up/shut down containers at will. So you can spin up a container to hit a specific URL in a second, scrape whatever you're looking for, then kill the container. This can be done via a job queue (sidekiq if you're using Ruby) to do all sorts of fun stuff.
That aside, hitting Insta like this is playing with fire, because you're really dealing with Facebook and their legal team.
Serious question: What do you gain from having an extra layer like docker?
Because you can use pre-packaged Selenium in Docker images with a few commands: https://github.com/SeleniumHQ/docker-selenium