In the following steps replace:
subdomain
with your desired subdomain.domain.com
with your domain.random.herokudns.com
with your Heroku DNS target (see step 1).
-
In the Heroku deployment settings, under domains, click “Add domain”. Enter
subdomain.domain.com
to receive therandom.herokudns.com
Heroku DNS target. -
In the Heroku deployment settings, under SSL certificates, ensure a certificate is automatically managed. If you don’t do this, attempting to visit
https://subdomain.domain.com
in a browser will fail with an SSL error. -
If you already aliased the subdomain to a Zeit Now deployment, use the Zeit Now CLI to remove the alias (I’m not sure what happens if you don’t do this):
now alias rm subdomain.domain.com
-
Add the
CNAME
DNS record so that the subdomain will be served by Heroku:now dns add domain.com subdomain CNAME random.herokudns.com
Within 60 seconds your Heroku deployment should serve https://subdomain.domain.com
.