When planning a cloud migration, don’t forget to plan ahead for IP address changes that could affect your workloads and the way they interact with internal and external network traffic.
Cloud providers and data centers have a limited pool of IP addresses that they own, and they often re-use previously assigned IPs in order to maximize them. You can’t simply move your existing IP addresses along with your services. Rather, you’ll receive a dynamically assigned internal and external IP address.
To complicate matters, you could lose those dynamically assigned IPs if you stop your cloud instance (but usually only if you stop and deallocate the VM resources — most providers will keep your IP assigned to you if your machine is paused/stopped but still reserved within the overall resource pool). Luckily, there are a few ways to keep IPs relatively static in the cloud.
When you move your application, database, or web server to a cloud host, you’ll have to reconfigure any connections that point to your old on-premise IP address — for example, firewall configurations or databases for apps that are hosted on a separate VM. This can grow quite tiresome and indeed unwieldy over large environments.
You should be able to purchase static IPs from your cloud provider. While this is an additional cost added on to your subscription, you can keep a stable IP address for any public facing services. Be sure to purchase these reserved IPs before setting up and configuring your VMs, so you can assign them accordingly.
A static IP should sit in front of your cloud servers, so any incoming traffic will point to your virtual data center. Incoming traffic is the directed by your load balancers accordingly. You can configure individual ports on each VM to better direct traffic to specific servers.
A key step is to update the DNS to reflect the new IP address within the cloud, so incoming public traffic is pointed to the cloud provider rather than the previous address. DNS servers can also work to reroute traffic to a dynamically assigned address, so long as incoming traffic is pointing to the domain name rather than a static IP.
There are also some third party software providers that allow you to choose your IP address and then assign cloud endpoints. You can change those endpoints on the fly while retaining your IP, so even if you move providers or your cloud provider changes your internal IP address, your public one remains the same.