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Manual Chapter: Introducing BIG-IP Device Service Clustering
Manual Chapter
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What is BIG-IP device service clustering?

Device service clustering, or DSC, is an underlying architecture within BIG-IP Traffic Management Operation System (TMOS), based on F5 Networks' ScaleN technology. DSC provides synchronization and failover of BIG-IP configuration data at user-defined levels of granularity, among multiple BIG-IP devices on a network. More specifically, you can configure a BIG-IP device on a network to:

  • Synchronize some or all of its configuration data among several BIG-IP devices
  • Fail over to one of many available devices
  • Mirror connections to a peer device to prevent interruption in service during failover

If you have two BIG-IP devices only, you can create either an active-standby or an active-active configuration. With more than two devices, you can create a configuration in which multiple devices are active and can fail over to one of many, if necessary.

By setting up DSC, you ensure that BIG-IP configuration objects are synchronized and can fail over at useful levels of granularity to the most-available BIG-IP devices on the network. You also ensure that failover from one device to another, when enabled, occurs seamlessly, with minimal to no interruption in application delivery.

The BIG-IP system supports either homogeneous or heterogeneous hardware platforms within a device group.

Important: If you use the Setup utility to create a DSC configuration, you can re-enter the utility at any time to adjust the configuration. Simply click the F5 logo in the upper-left corner of the BIG-IP Configuration utility, and on the Welcome screen, click Run Config Sync/HA Utility.

DSC components

Device service clustering (DSC) is based on a few key components.

Devices
A device is a physical or virtual BIG-IP system, as well as a member of a local trust domain and a device group. Each device member has a set of unique identification properties that the BIG-IP system generates.
Device groups
A device group is a collection of BIG-IP devices that trust each other and can synchronize, and sometimes fail over, their BIG-IP configuration data. You can create two types of devices groups: A Sync-Failover device group contains devices that synchronize configuration data and support traffic groups for failover purposes when a device becomes unavailable. A Sync-Only device group contains devices that synchronize configuration data, such as policy data, but do not synchronize failover objects.
Traffic groups
A traffic group is a collection of related configuration objects (such as a virtual IP address and a self IP address) that run on a BIG-IP device and process a particular type of application traffic. When a BIG-IP device becomes unavailable, a traffic group can float to another device in a device group to ensure that application traffic continues to be processed with little to no interruption in service.
Device trust and trust domains
Underlying the success of device groups and traffic groups is a feature known as device trust. Device trust establishes trust relationships between BIG-IP devices on the network, through mutual certificate-based authentication. A trust domain is a collection of BIG-IP devices that trust one another and is a prerequisite for creating a device group for config sync and failover operations. The trust domain is represented by a special system-generated and system-managed device group named device_trust_group, which is used to synchronize trust domain information across all devices.
Folders
Folders are containers for the configuration objects on a BIG-IP device. For every administrative partition on the BIG-IP system, there is a high-level folder. At the highest level of the folder hierarchy is a folder named root. The BIG-IP system uses folders to affect the level of granularity to which it synchronizes configuration data to other devices in the device group.

Best practices

F5 Networks recommends that you follow these best practices when deploying a DSC configuration:

Licensing and module provisioning
Verify that the licensing and the module provisioning is equivalent on all devices in the device group.
Traffic group load and device capacity
For a Sync-Failover device group, verify that the device with the smallest capacity has the capacity to process all traffic groups. This ensures application availability in the event that all but one device in the device group become unavailable for any reason.
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