Ok, this took me a while to figure out. Let's keep it short and to the point:
How you add a custom domain to App Runner in 5 steps
- Move the DNS of your domain to Route 53. Yes, I tried it with Cloudflare but I didn't get it to work.
- Go to your App Runner service and go to the tab custom domains. Enter your domain name in the popup: e.g. grafiki.cc.
- You will see a table with DNS records you have to create. The certificate validation records are CNAME records, the DNS target i an A-record that you can point to an ALIAS.
4. The CNAME records are easy to set up, to add the DNS target, this is what it should look like:
a) Check that record type is A
b) Check "Alias"
c) We want to alias an AppRunner service, and then in the dropdown below check your region. The choose your app on AppRunner.
5. Now you have to wait till the certificates from ACM are validated. In my case this took 4 hours.