A Reserved IP in DigitalOcean isn’t just a static IP; it’s a network interface that can be detached and reattached to different Droplets, effectively letting you move your IP address between servers without reconfiguring DNS.
Let’s see this in action. Imagine we have a web server Droplet, web-prod-1, currently running on 192.168.1.10. We want to upgrade it to a new, more powerful Droplet, web-prod-2, but we don’t want to update our DNS records for example.com if we can avoid it.
First, we need to create a Reserved IP. From the DigitalOcean control panel, navigate to "Networking" and then "Reserved IPs." Click "Assign Reserved IP." You’ll choose the region where you want to assign it. Let’s say we choose the "New York 3" datacenter. DigitalOcean will provision a new IP address for you, say 167.99.10.20. This IP is now associated with your account but not yet with any specific Droplet.
Now, we assign this Reserved IP to our existing web-prod-1 Droplet. From the Droplet’s page, under "Networking," you’ll see an option to "Assign Reserved IP." Select the 167.99.10.20 IP address from the dropdown. DigitalOcean handles the underlying network configuration. On web-prod-1, the operating system will now have 167.99.10.20 as one of its IP addresses, alongside its original private IP. If you were to SSH into web-prod-1 and run ip addr show, you’d see both.
The magic happens when we need to perform maintenance or upgrade. We’ll power down web-prod-1. Then, we go back to the "Networking" section of web-prod-1 or the "Reserved IPs" list, and we select "Detach" for 167.99.10.20. This frees up the IP address from the old Droplet.
Next, we’ll create our new Droplet, web-prod-2. Once it’s provisioned and running, we navigate to its "Networking" section and choose "Assign Reserved IP." This time, we select 167.99.10.20 from the list of available Reserved IPs. DigitalOcean immediately routes traffic destined for 167.99.10.20 to the new web-prod-2 Droplet.
Crucially, if example.com’s A record pointed to 167.99.10.20, no DNS changes are necessary. The switch is effectively instantaneous from the perspective of your domain’s public IP.
The underlying mechanism involves DigitalOcean’s network infrastructure. When you assign a Reserved IP, it’s an IP address managed by DigitalOcean’s network fabric. Attaching it to a Droplet means that Droplet’s network interface gets configured to respond to ARP requests for that IP and to receive traffic directed to it. Detaching it removes that configuration, and reattaching it applies it to a new interface. This is all managed at the hypervisor and network switch level within their data centers, abstracting away the need for manual network interface configuration within the Droplet’s OS itself, beyond what the cloud-init or initial setup might do.
The primary benefit is seamless IP address continuity. This is invaluable for services that require a stable, publicly routable IP address, such as authoritative DNS servers, mail servers, or any service whose IP is hardcoded in critical external systems. It also simplifies disaster recovery scenarios; if a Droplet fails, you can quickly spin up a replacement and reassign the Reserved IP without impacting your clients’ ability to reach your service.
While a Reserved IP is publicly routable, it doesn’t inherently come with inbound firewall rules configured within DigitalOcean’s cloud firewall. You’ll still need to ensure your Droplet’s firewall (like ufw or iptables) and your DigitalOcean Cloud Firewall rules are correctly configured to allow traffic to the Reserved IP.
The next step after mastering Reserved IPs is understanding Floating IPs, which are similar but have slightly different use cases, particularly around high availability and failover within specific regions.