If Heruku fails to build and complains about:

Compiled slug size: 500.3M is too large (max is 500M)

you may Google and find the ThoughtBot article which suggests:

# This command DOES NOT clear build cache
$ heroku repo:purge_cache --app your-app-name

Even after running the command, the build size didn’t get reduced at all.

Instead, the Heroku official answer has the CORRECT command:

$ heroku plugins:install heroku-builds
$ heroku builds:cache:purge --app your-app-name

What confused me was the CLI documentation about heroku repo:purge_cache is

This will delete the contents of the build cache stored in the repository.

while heroku builds:cache:purge doc says:

purge the build cache for the specified app

But only the latter does its job well.

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Junji Zhi

Senior Software Engineer.