F5 Device Service Clustering

--> Device Service Clustering is a method of combining two or more physical F5 devices into one logical device.

--> Device Service Clustering basically used to provide high availability to the Virtual Servers.

--> In order to understand high availability in F5 we need to understand following terms,

i) Device Group 

--> Collections of F5 devices that can share configuration and objects with each other in the cluster. Device Group can be either sync-only or sync-failover.

--> Each and every device in the Device group contains device certificate installed on it.

--> Devices in the Device group share certificates to establish the trust relationship between them to exchange configuration and policies.

--> sync-only Device Group contains the devices that synchronize only configuration data and does not support failover between the devices.

--> For example, you can use a Sync-Only device group to synchronize a folder containing policy data that you want to share across all BIG-IP devices in a local trust domain. A Sync-Only device group supports a maximum of 32 devices.

--> sync-failover Device Group contains the devices that synchronize configuration data as well as support failover between the devices.

--> We will use sync-failover Device Group in the case of High Availability.

--> A Sync-Failover device group supports a maximum of eight devices.

--> Before creating the device group, you should configure the configuration synchronization (ConfigSync) and Failover IP addresses for each BIG-IP system in the device group.

--> The ConfigSync address is the IP address that the system uses when synchronizing configuration with peer devices, and the Failover address is the IP address that the system uses for network failover.

-->  F5 considers it best practice to select both the management address and a Traffic Management Microkernel (TMM) network address to use for network failover.

ii) Traffic Group

--> Traffic Group determines how the traffic need to be forwarded between the devices in the device group.

--> In general, a traffic group ensures that when a device becomes unavailable, all of the failover objects in the traffic group fail over to any one of the devices in the device group, based on the number of active traffic groups on each device.

--> Although a specific traffic group can be active on only one device in a device group and all the other devices in the device group will be in standby state.

--> When a traffic group fails over to another device in the device group, the device that the system selects is normally the device with the least number of active traffic groups.

-->  When you initially create the traffic group on a device, however, you specify the device in the group that you prefer that traffic group to run on in the event that the available devices have an equal number of active traffic groups (that is, no device has fewer active traffic groups than another).

--> Note that, in general, the system considers the most available device in a device group to be the device that contains the fewest active traffic groups at any given time.

-->  A Sync-Failover device group can support a maximum of 15 traffic groups.

Reference: F5