Heroku App connected to subdomain in Netlify DNS


I have a created a small app on Heroku which is on a default Heroku domain

I want this domain to be a subdomain of my main project which is hosted on my Netlify account.
Thus, my heroku app should be available at portal.kassebil.dk.

I thought it would be as easy as just creating a CNAME record in Netlify DNS at portal.kassebil.dk pointing towards the value I got from Heroku which is:


However, this does not seem to work for me. What am I doing wrong here?


The setup seems to be correct. If you have setup everything else correctly on Heroku end, it should work. Not sure, but maybe you can try asking this to Heroku support also (if you haven’t already).

I’m having the exact same issue. I added a CNAME in Netlify to point to the Heroku DNS Target (some-very-long-URL.herokudns.com) but I’m getting a 400 when I try to access the admin panel through this new subdomain. Any idea why?

Hi, @kevinloupe. Did you add the custom domain to the site at Heroku? If so, would you please show us a screenshot of what you added there?

If not, adding it to the Heroku site should resolve this.

Hi Luke, thanks for following up. I got it resolved: it was because I was running a Django app on Heroku and I didn’t add the new CNAME (api.loupehealth.com) to the ALLOWED_HOSTS for my Django (an env var). Once I did, it worked.

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Thanks for sharing the steps taken to fix it! This really helps other people searching here in the future and our support team thanks you for taking the time to come back here to share this information!