How do I know I have an incorrect custom hostname DNS configuration?

Issue

You want to verify your DNS configuration and determine if your current setup is incorrect

Resolution

Heroku started appending identifiers to subdomains on June 14, 2023. Applications created before this date follow the old subdomain scheme where the subdomain was the same as the app name.

We encourage you to check that custom domain DNS records are configured with the DNS CNAME target listed by Heroku as per the Custom Domain Dev Center documentation. We’re prioritizing upgrading apps that we can determine are correctly configured first, but all apps will be upgraded over the coming months.

Here are examples of incorrect setups that may work with previous-generation Common Runtime infrastructure but will break when an app is upgraded:

• DNS record for foo-app custom domain pointed at bar-app.herokuapp.com (DNS record for domain associated with foo-app and pointed at foo-app.herokuapp.com should also be updated to use the DNS target provided by Heroku, although the foo-app.herokuapp.com will continue to work as a target for upgraded apps)
• DNS record for custom domain associated with foo-app pointed at SSL Endpoint CNAME target associated with bar-app. The SSL Endpoint add-on has been deprecated and existing users will be migrated to Heroku SSL, a more flexible cost-effective and modern TLS-termination option.
• Custom domains on review apps with DNS entries pointed at parent/production app’s haiku.herokudns.com target, app.herokuapp.com target, or proxy.herokuapp.com
• Creating a wildcard (*.your-domain.com) DNS entry pointed at a Heroku DNS target and relying on that to support custom domains associated with other Heroku apps