3.5. Defining cluster policies
Until now, you have worked without a specific cluster policy. The virtual machines were started on a host selected on round robin logic; as long as there are available resources on the host, virtual machines can be migrated onto it. Furthermore, there was no load balancing of running virtual machines. For example, a virtual machine will remain on the host it was run initially unless it is specifically moved, either by user triggered migration (maintenance mode or manual virtual machine migration) or by a system high availability event (this will be explained in the advanced High Availability lab). Cluster policy allows you to better control the scheduling of virtual machines and to perform load balancing.
Two types of policies are available:
- Even Distribution: You can set a maximum service level threshold for the hosts in the cluster. If a host is above the threshold, then the Red Hat Enterprise Virtualization Manager will live migrate virtual machines off this host to other hosts in the cluster, as long as the other hosts' loads are below this threshold. This affects the scheduling of running new machines in a similar manner.
- Power Saving: This is a superset of the even distribution policy. A low threshold is set for consolidating virtual machines. If a server in the cluster drops below the threshold, then the virtual machines on this server are live migrated to other servers in the cluster, as long as the other servers are not above the maximum service level threshold.
In the following example you will set and test both thresholds.
Procedure 3.1. Setting Load and Power Management Policies for Hosts
- Use the resource tabs, tree mode, or the search function to find and select the cluster in the results list.
- Click the button to open the Edit Cluster window.
- Select one of the following policies:
- None
- Evenly_Distributed - Enter CPU utilization percentage at which virtual machines start migrating to other hosts in the HighUtilization text field.
- Power Saving - Enter the CPU utilization percentage below which the host will be considered under-utilized in the LowUtilization text field. Enter the CPU utilization percentage at which virtual machines start migrating to other hosts in the HighUtilization text field
- Specify the time interval in minutes at which the selected policy will be triggered in the CpuOverCommitDurationMinutes text field.
- If you are using an OpenAttestation server to verify your hosts, and have set up the server's details using the
engine-configtool, select the Enable Trusted Service check box. - Click .
Now you can test these new settings. After the maintenance lab you now have a host (Atlantic) that does not have any virtual machines running. Select one of the Red Hat Enterprise Linux virtual machines and load it, then watch as the hosts in the cluster balance the virtual machines' workloads.