Cloud Failover Extension Overview

The F5 BIG-IP Cloud Failover Extension (CFE) is an iControl LX extension that provides L3 failover functionality in cloud environments, effectively replacing Gratuitous ARP (GARP). CFE uses a declarative model, meaning you provide a JSON declaration using a single REST API call rather than a set of imperative commands. The declaration then configures the BIG-IP system with all the required settings for cloud failover. At a high level, to use CFE, you will download the RPM from GitHub, upload the RPM to BIG-IP, tag or label your cloud resources, and then Post your declaration.


How does it work?

In the event of a failover between BIG-IP systems, BIG-IP fails a traffic group over, which runs the /config/failover/tgactive script. CFE updates that file during any configuration request to ensure it triggers failover by calling the Cloud Failover /trigger API. During a failover event, CFE then moves or updates cloud resources as described below:

  • Failover IP(s): The extension updates IP configurations between NICs, updates EIP/private IP associations, and updates forwarding rule target instances.
  • Failover Routes: The extension updates Azure User-Defined Routes (UDR), AWS route tables, and GCP forwarding rule targets to point to a self IP address of the active BIG-IP device.
  • Failback: The extension reverts to using the designated primary BIG-IP when it becomes active again.

The diagram below shows a typical failover scenario for an active/standby pair of BIG-IPs in a cloud environment. To see how Cloud Failover Extension works in specific cloud environments, see the sections for AWS, Azure, and Google Cloud.


Why use Cloud Failover Extension?

Using Cloud Failover Extension has three main benefits:

  • Standardization: Failover patterns will look similar across all clouds.
  • Portability: You can leverage a variety of methods, including cloud-native templates, Terraform, and Ansible, to install and run CFE.
  • Lifecycle and Supportability: You can upgrade BIG-IP without having to call F5 support to fix failover.


To provide feedback on Cloud Failover Extension or this documentation, you can file a GitHub Issue.