Subdomains On The Fly, but different IPs

My team and I are creating a service that when user request, it creates a new server instance on the fly, with a different IP for each new instance. The issue is that I’m connecting from a client via WebSockets to that newly created server. But I need it to be SSL certificated. So I can’t use just the IP.

So, what I’m thinking is to create a subdomain for each one of this server instances. The only issue here is that I need the subdomain to be available super quick, and I don’t know if I can trust the DNS propagation times for this.

Is there any solution to this? Like having my own routing server that have a Wildcard Subdomain and then route the traffic based on that? I think I can’t use Apache or those kind of solutions because it’s not only HTTP/S traffic that I’m handling.