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Capacity Planning

Contrail Insights Plan helps you understand, plan, and model the capacity of your infrastructure. Figure 1 shows the allocated capacity charts and availabile capacity table.

Figure 1: Allocated Capacity Charts and Available Capacity TableAllocated Capacity Charts and Available Capacity Table

Allocated Capacity

In OpenStack, the unit of compute resource allocation is an instance of a particular flavor. A flavor defines the amount of virtual central processing units (vCPUs), memory, and local storage allocations for an instance.

In the Plan pane of the Dashboard, a pie chart indicates the current number of allocated instances on a per-flavor basis. This provides an operator with an understanding of the types of resources requested by users of the infrastructure.

To understand the change in capacity over time, line charts show the history of allocated and available capacity in terms of the number of instances of each flavor type. Using the drop-down list, you can choose to see the used, available, or peak capacities of the infrastructure. Each line on the chart represents one flavor type. The time period displayed by the charts is configurable to view trends over long or short time horizons, and plan for appropriate resource capacity.

Allocated capacity is also displayed on a per-resource basis. The allocated percentage of capacity is displayed for compute, memory, and storage resources.

Available Capacity

The available capacity table shows the number of instances of each flavor type that can be allocated presently. The available capacity takes into consideration the resource requirements of each flavor type, the current unused capacity of the physical infrastructure, and the scheduler policy that constrains which sets of hosts can be used to allocate an instance of a particular flavor.

Modeling Oversubscription Policy

The oversubscription policy of the OpenStack Nova scheduler affects the available capacity of the infrastructure. In Settings > Oversubscription, Contrail Insights has a configuration for oversubscription ratios. Contrail Insights uses these ratios when calculating the available capacity. The ratios configured in Contrail Insights do not affect the configuration of the scheduler.

You can modify the ratios to model how an oversubscription policy will affect the available capacity of the infrastructure. When the ratios are modified, the available capacity table will update to show how many instances of each flavor type may be allocated. By configuring different modeling ratios, an administrator can see the impact of potential changes to the oversubscription policy of the scheduler, or understand how increasing physical capacity in the areas of compute, memory, and storage will address the demands of users.

Upon initial installation, the oversubscription ratios in Contrail Insights are set to 1 (that is, no oversubscription). When not modeling a policy change, we recommend configuring the ratios to match the configuration of the OpenStack Nova scheduler policy so the available capacity table reflects the actual capacity of the infrastructure.