When I provision a new container or virtual machine to serve an application, I let my Ubiquiti router's DHCP server hand them an IP. I already have to manage some static IP assignments for things like my PostgreSQL cluster or Kubernetes nodes, so letting machines that don't need static IPs get one assigned is helpful to my mental load. And generally since these machine are long-running (rarely shut down), the IP reservation the router hands to them sticks around. It sticks around long enough, anyways, that I get comfortable assuming it's basically static and end up relying on it being the same always. This is, of course, wrong, but I did it anyways.