A Sync-Failover device group contains devices that synchronize their configuration data and fail over to one another when a device becomes unavailable. A Sync-Failover device group supports a maximum of eight devices.

traffic_group_1 is active on a device in a Sync-Failover device group

On failover, traffic_group_1 becomes active on another device in the Sync-Failover device group

For devices in a Sync-Failover group, the BIG-IP system uses both the device group and the traffic group attributes of a folder to make decisions about which devices to target for synchronizing the contents of the folder, and which application-related configuration objects to include in failover.

You can control the way that the BIG-IP chooses a target failover device. This control is especially useful when a device group contains heterogeneous hardware platforms that differ in load capacity, because you can ensure that when failover occurs, the system will choose the device with the most available resource to process the application traffic.

1. On the Main tab, click Device Management > Device Groups .
2. On the Device Groups list screen, click Create.
   The New Device Group screen opens.
3. In the Name field, type a name for the device group.
4. From the Group Type list, select Sync-Failover.
5. In the Description field, type a description of the device group.
   This setting is optional.
6. From the Configuration list, select Advanced.
7. For the Members setting, select a host name from the Available list for each BIG-IP device that you want to include in the device group, including the local device. Use the Move button to move the host name to the Includes list.
   The Available list shows any devices that are members of the device's local trust domain but not currently members of a Sync-Failover device group. A device can be a member of one Sync-Failover group only.
8. From the Sync Type list:
   • Select Automatic with Incremental Sync when you want the BIG-IP system to automatically sync the most recent BIG-IP configuration changes from a device to the other members of the device group. In this case, the BIG-IP system syncs the configuration data whenever the data changes on any device in the device group.
   • Select Manual with Incremental Sync when you want to manually initiate a config sync operation. In this case, the BIG-IP system syncs the latest BIG-IP configuration changes from the device you choose to the other members of the device group. We strongly recommend that you perform a config sync operation whenever configuration data changes on one of the devices in the device group.
   • Select Manual with Full Sync when you want to manually initiate a config sync operation. In this case, the BIG-IP system syncs the full set of BIG-IP configuration data from the device you choose to the other members of the device group. We strongly recommend that you perform a config sync operation whenever configuration data changes on one of the devices in the device group.
9. In the Maximum Incremental Sync Size (KB) field, retain the default value of 1024, or type a different value.
   This value specifies the total size of configuration changes that can reside in the incremental sync cache. If the total size of the configuration changes in the cache exceeds the specified value, the BIG-IP system performs a full sync whenever the next config sync operation occurs.
10. For the Network Failover setting, select or clear the check box:
    • Select the check box if you want device group members to handle failover communications by way of network connectivity. This is the default value and is required for active-active configurations.
    • Clear the check box if you want device group members to handle failover communications by way of serial cable (hard-wired) connectivity.
    For active-active configurations, you must select network failover, as opposed to serial-cable (hard-wired) connectivity.
11. In the Link Down Time on Failover field, use the default value of 0.0, or specify a new value.
    This setting specifies the amount of time, in seconds, that interfaces for any external VLANs are down when a traffic group fails over and goes to the standby state. Specifying a value other than 0.0 for this setting causes other vendor switches to use the specified time to learn the MAC address of the newly-active device.

    Important: This setting is a system-wide setting, and does not apply to this device group only. Specifying a value in this field causes the BIG-IP system to assign this value to the global bigdb variable failover.standby.linkdowntime.
12. Click Finished.

1. On the Main tab, click Device Management > Device Groups .
2. In the Group Name column, click the name of the relevant device group.

1. On the Main tab, click Device Management > Device Groups .
2. In the Group Name column, click the name of the relevant device group.
3. In the Members area of the screen, select a host name from the Available list for each BIG-IP^® device that you want to include in the device group. Use the Move button to move the host name to the Selected list.
   The Available list shows any devices that are members of the device's local trust domain but not currently members of a Sync-Failover device group. If you are attempting to add a member to a Sync-Failover group and you do not see the member name in the list, it is possible that the device is already a member of another Sync-Failover device group. A device can be a member of one Sync-Failover group only.
4. Click Update.
5. On the Main tab, click Device Management > Overview .
6. In the Devices area of the screen, make sure that the device you are logged into is selected.
7. In the Sync Options area of the screen, click Push the selected device configuration to the group.

Sometimes when one BIG-IP^® object references another, one of the objects gets synchronized to a particular device, but the other object does not. This can result in an invalid device group configuration.

For example, suppose you create two device groups that share some devices but not all. In the following illustration, Device A is a member of both Device Group 1 and Device Group 2.

One device with membership in two device groups

Device Group 1 is associated with folder /Common, and Device Group 2 is associated with the folder /Common/my_app. This configuration causes Device A to synchronize all of the data in folder /Common to Device B in Device Group 1. The only data that Device A can synchronize to Device C in Device Group 2 is the data in the folder /Common/my_app, because this folder is associated with Device Group 2 instead of Device Group 1.

Now suppose that you create a pool in the /Common/my_app folder, which is associated with Device Group 2. When you create the pool members in that folder, the BIG-IP system automatically creates the associated node addresses and puts them in folder /Common. This results in an invalid configuration, because the node objects in folder /Common do not get synchronized to the device on which the nodes' pool members reside, Device C. When an object is not synchronized to the device on which its referenced objects reside, an invalid configuration results.