By Neha Pattan, Staff Software Engineer; Ines Envid, Product Manager

High availability and redundancy are essential features for a cloud deployment. On Google Cloud Platform (GCP), Alias IPs allow you to configure secondary IPs or IP ranges on your virtual machine (VM) instances, for a secure and highly scalable way to deliver traffic to your applications. Today, we’re excited to announce that you can now dynamically add and remove alias IP ranges for existing, running VMs, so that you can migrate your applications from one VM to another in the event of a software or machine failure.

In the past, you could deploy highly available applications on GCP by using static routes that point to a hosted Virtual IP (VIP), plus adjusting the next-hop VM of that VIP destination based on availability of the application hosting the VM. Now, Alias IP ranges support hot standby availability deployments, including multiple standbys for a single VM (one-to-many), as well as multiple standbys for multiple VMs (many-to-many).
With this native support, you can now rely on GCP’s IP address management capabilities to carve out flexible IP ranges for your VMs. This delivers the following benefits over high-availability solutions that use static routes:

• Improved security: Deployments that use Alias IP allow us to apply anti-spoofing checks that validate the source and destination IP, and allow any traffic with any source or destination to be forwarded. In contrast, static routes require that you disable anti-spoof protection for a VM.
• Connectivity through VPN / Google Cloud Interconnect: Highly available application VIPs implemented as Alias IP addresses can be announced by Cloud Router via BGP to an on-premises network connected via VPN or Cloud Interconnect. This is important if you are accessing the highly available application from your on-premises data center.
• Native access to Google services like Google Cloud Storage, BigQuery and any other managed services from googleapis.com. By using Alias IP, highly available applications get native access to these services, avoiding bottlenecks created by an external NAT proxy.

Let’s take a look at how you can configure floating Alias IPs.

Imagine you need to configure a highly available application that requires machine state to be constantly synced, for example between a database master and slave running on VMs in your network. Using Internal Load Balancing doesn’t help here since the traffic needs to be sent to only one server. With Alias IPs, you can configure your database to run using secondary IPs on the VM's primary network interface. In the event of a failure, you can dynamically switch this IP to be removed from the bad VM and attach it to the new server.

This approach is also be useful if an application in your virtual network needs to be accessed across regions, since Internal Load Balancing currently only supports only in-region access.

You can use Alias IP from the gcloud command line interface.

To migrate 10.10.0.5 from VM-A to VM-B
a) Remove the IP from VM-A

gcloud compute instances network-interfaces update \
     virtual-machine-a --zone us-central1-a --aliases 

b) Add the IP to VM-B

gcloud compute instances network-interfaces update \
     virtual-machine-b --zone us-central1-a \
     --aliases “range1:10.10.0.5”

In addition to adding and removing alias IPs from running VMs, you can create up to 10 Alias IP ranges per network interface, including up to seven secondary interfaces attached to other networks.
You can also use Alias IP with applications running within containers and being managed by container orchestration systems such as Kubernetes or Mesos. Click here to learn more about how Kubernetes uses Alias IPs.

Being able to migrate your workloads while they are running goes a long way toward ensuring high availability for your applications. Drop us a line about how you use Alias IPs, and other networking features you’d like to see on GCP.