2.8 KiB
Capacity planning
An important consideration in running a cloud over time is projecting growth and utilization trends in order to plan capital expenditures for the short and long term. Gather utilization meters for compute, network, and storage, along with historical records of these meters. While securing major anchor tenants can lead to rapid jumps in the utilization rates of all resources, the steady adoption of the cloud inside an organization or by consumers in a public offering also creates a steady trend of increased utilization.
Capacity constraints for a general purpose cloud environment include:
- Compute limits
- Storage limits
A relationship exists between the size of the compute environment and the supporting OpenStack infrastructure controller nodes requiring support.
Increasing the size of the supporting compute environment increases the network traffic and messages, adding load to the controller or networking nodes. Effective monitoring of the environment will help with capacity decisions on scaling.
Compute nodes automatically attach to OpenStack clouds, resulting in a horizontally scaling process when adding extra compute capacity to an OpenStack cloud. Additional processes are required to place nodes into appropriate availability zones and host aggregates. When adding additional compute nodes to environments, ensure identical or functional compatible CPUs are used, otherwise live migration features will break. It is necessary to add rack capacity or network switches as scaling out compute hosts directly affects network and datacenter resources.
Compute host components can also be upgraded to account for increases in demand; this is known as vertical scaling. Upgrading CPUs with more cores, or increasing the overall server memory, can add extra needed capacity depending on whether the running applications are more CPU intensive or memory intensive.
Another option is to assess the average workloads and increase the number of instances that can run within the compute environment by adjusting the overcommit ratio.
Note
It is important to remember that changing the CPU overcommit ratio can have a detrimental effect and cause a potential increase in a noisy neighbor.
Insufficient disk capacity could also have a negative effect on overall performance including CPU and memory usage. Depending on the back-end architecture of the OpenStack Block Storage layer, capacity includes adding disk shelves to enterprise storage systems or installing additional block storage nodes. Upgrading directly attached storage installed in compute hosts, and adding capacity to the shared storage for additional ephemeral storage to instances, may be necessary.
For a deeper discussion on many of these topics, refer to the OpenStack Operations Guide.