App Platform: Set subdomain to redirect to folder on main domain

Hi there,

DNS can only map hostnames to IPs or other hostnames. It does not know anything about paths like /foo, so doing foo.example.com to example.com/foo purely with a CNAME generally is not possible.

Since you are on App Platform, this likely has to be handled at the application or proxy level, not in DNS.

One option, if you control the app code, is to check the Host header for foo.example.com and return a 301 redirect to https://example.com/foo. That approach works in most frameworks.

Another possible option is to route things internally so that requests coming to foo.example.com are served from /foo, but that usually requires more custom proxy logic and is not always needed.

As far as I know, App Platform does not currently have a built-in DNS-level feature to redirect a subdomain to a path on another domain. The URL rewrite feature is for paths on the same host, not for mapping different hosts.

So in practice, the custom domain setup plus an app-level redirect is usually the safest way to do this.

Heya, @huntybunz

You can’t do this with DNS. A CNAME can only point to a hostname, not a URL path, so example.com/foo will always fail.

You need to add a redirect inside your app on App Platform. Attach foo.example.com to the app, then in your app code or framework config return a 301 redirect to /foo.

Regards