herokuapp.com subdomain names are changing
Change effective on 25 May 2023
Starting June 14, 2023, new apps get a randomly generated 12-character identifier appended to the subdomain portion of the built-in APPNAME.herokuapp.com domains.
The new format is APPNAME-IDENTIFIER.herokuapp.com, for example, example-app-1234567890ab.herokuapp.com. The generated value isn’t added to the app name itself, only to the subdomain. Runtime Dyno Metadata includes this new identifier as HEROKU_APP_DEFAULT_DOMAIN_NAME.
We’re making this change to avoid domain takeovers when apps are deleted or renamed. The change applies to new apps created on and after June 14th. Existing applications created prior to this date aren’t impacted. Review Apps and Heroku CI apps also aren’t impacted.
To learn more about this change, see Heroku App Names and Subdomains.