What is the F5 Cloud Failover Extension?
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Overview
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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.

To use CFE, you must install the RPM package, tag/label your cloud resources, and then Post your declaration.

.. image:: ./images/cfe-overview-steps.png
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How does it work?
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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 Azure, AWS, and Google Cloud.


.. image:: ./images/cfe-diagram.gif
   :align: left

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Why use Cloud Failover Extension?
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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 BIG-IP Runtime Init, cloud-native templates, Terraform, and Ansible to install and run CFE.
- Lifecycle and Supportability: You can upgrade BIG-IPs without having to re-configure HA failover.