Just add an index.php to your repository. It tells Heroku that the site is a PHP site and that it will be hosted using
And yes, you can still have an index.html file. The .html file takes precedence over the .php one. Have fun!
You have just read Hosting static sites in Heroku, written on March 10, 2015. This is Today I Learned, a collection of random tidbits I've learned through my day-to-day web development work. I'm Rico Sta. Cruz, @rstacruz on GitHub (and Twitter!).