Limiting IP Movement in a Cluster

In a probe cluster, unassigned IPs are assigned to the cluster's Probes in such a way that the imbalance IP ratio among the Probes remains at a minimum. The imbalance ratio is governed by the imbalance threshold.

Changing the cluster's network range, changing the set of Probes associated with the cluster, or assigning a TQL constraint on a Probe in the cluster can cause an imbalance of IPs among the Probes in the cluster.

In such a situation, and depending on the IP imbalance threshold, the cluster attempts to re-balance the IPs among the cluster's Probes. That is, if one of the Probes violates the average number of IPs per Probe, as defined by the imbalance threshold, the cluster re-balances the IPs. If not, the cluster leaves the current IP distribution unchanged.

Example:

If a cluster has 5 Probes and 1000 IPs in its range, the average number of IPs per Probe should be 200.

If the imbalance threshold is set to 20%, then if each of the Probes has between 160-240 IPs, they do not violate the imbalance threshold, and no re-balancing is necessary.

If, however, there are Probes with less than 160 IPs, or more than 240 IPs (see image below)—that is, more than a 20% deviation from the average 200—the cluster attempts to re-balance the IPs among the Probes—as long as the TQL constraints on the Probes allow this.

For details on how to specify the imbalance threshold, see How to Limit IP Movement in a Cluster.