Why do "heroku run" commands get stuck for apps built in docker containers?

Issue

heroku run commands hang and show connecting... indefinitely for an app built with the container stack.

Resolution

If your app does not have a container image named web you will need to manually specify the name of the image with the run command like:

heroku run bash --type worker -a <app_name>

For applications build with a heroku.yml file, you can check to see your app defines a web image:

  docker:
    web: Dockerfile
    worker: Dockerfile

View our documentation for more details on how container apps are run:
https://devcenter.heroku.com/articles/container-registry-and-runtime#one-off-dynos.