F5 Cloud Failover

Welcome to the F5 Cloud Failover Extension User Guide. To provide feedback on this documentation, you can file a GitHub Issue.


The F5 Cloud Failover Extension (CFE) is an iControl LX extension that provides L3 failover functionality in cloud environments, effectively replacing Gratuitous ARP (GARP). Cloud Failover Extension uses a declarative model, meaning you provide a JSON declaration using a single REST API call. The declaration represents the configuration that Cloud Failover Extension is responsible for creating on a BIG-IP system.

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. The Cloud Failover Extension 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 an Azure cloud environment. To see how Cloud Failover Extension works in other cloud environments, see the corresponding sections for AWS 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.

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