All applications automatically get assigned a subdomain on your AppPack cluster. When setting up your cluster, AppPack will create a wildcard DNS record which points all subdomains to the cluster's load balancer. A wildcard TLS certificate will also be created and attached to the load balancer.
For example, if you setup a cluster with the domain,
cluster.example.com, any app you create in that cluster will be available via
<appname>.cluster.example.com. So an app named
my-app will get assigned the domain
It's also possible to setup custom domains to attach a vanity domain to your application.