heroku:container push with buildx (set platform)

[gcatanese]

Feature

What is the current behavior?

When pushing from a Mac M1 (heroku container:push web) the default Docker driver is used (arm) but this does not deploy

Error: Exec format error
Process exited with status 126

Workarounds are:

• set DOCKER_DEFAULT_PLATFORM export DOCKER_DEFAULT_PLATFORM=linux/amd64 before pushing

• build with buildx (docker buildx build --platform linux/amd64 -t myname .) setting the platform, tag and push the image

What is the expected behavior?

It would be useful to pass the platform as additional parameter and use buildx

heroku version: heroku/7.50.0 darwin-x64 node-v12.16.2 MacBook Pro BigSur No HTTP or proxu