Docker "Failed to open TCP connection to 127.0.0.1:4444" when running selenium/capybara test in container
It's not easy to say without seeing your specs but I'm guessing you connect to selenium on 127.0.0.1:4444 in your tests?
If so you should now connect to it on hub:4444 as that is the name which will resolve to the IP of your selenium hub container.