About group leaders and group members

Definition of group leader and group member

CDAs that receive content directly from the ContentDirector core application are called group leaders. Group leaders distribute content to other CDAs called group members. Typically, group members are located at the periphery of your network and are the ultimate recipients of the pushed content.

Note
Group leaders can be configured as assigned group leaders or candidate group leaders. See Properties of group leaders for information about group leader assignments.

How group leader and group member assignments are used to distribute content

When you configure a CDA, you must specify the role it is to assume in the ContentDirector deployment. By configuring a CDA as a group leader or group member, you define the ContentDirector transport hierarchy (also called transport groups).

CDAs configured as group leaders communicate with their respective group members to determine the operational state of all devices in the group. After compiling this status information, the group leader sends it to the core application so that each device can be represented in the ContentDirector management console for grouping and scheduling purposes.

Administrators then use the ContentDirector management console to assign group leaders and group members to specific destination groups, which define the logical subset of CDAs that will receive the specified content. A destination group can consist of one or more transport groups. For example, a single content group created to distribute content to three remote branch offices could use multiple transport groups to distribute the content.

Group leader and group member configuration options

There are two configuration options for group leaders and group members:

Group leader and group member on the same device
Group leader and group member on separate devices

The illustration below shows both options.

Properties of group leaders

There are two types of group leaders: assigned and candidate.

Assigned group leaders automatically become the group leader for the transport group. (A transport group is a set of CDAs on one or more subnets that can join the same multicast group.) Create only one assigned group leader per segment to avoid conflicting group leader claims.
Candidate group leaders are on failover standby in case the assigned group leader cannot fulfil its function. If the assigned group leader fails, the candidate group leaders negotiate which machine assumes the group leader role through an election process.

For maximum reliability, designate a minimum of two group leaders whenever possible. The recommended configuration is one assigned group leader and one candidate group leader.

It is not necessary to have an assigned group leader in each transport group. If there is no assigned leader, the leader is elected from the pool of candidates. It takes less time for the core application to recognize the transport group at startup if you assign a group leader, rather than requiring elections among candidates.