CPU entitlement in cloud.gov

Cloud Foundry (the software cloud.gov uses) reports a "cpu" metric on apps. Unfortunately this metric is misleading; it tells us how much CPU an app is using as a percentage of the virtual host's CPU. Typically an app shares that CPU with other apps, so this metric doesn't help us much. For example:

• Less CPU is available to an app when other apps on the same host are using CPU
• Cloud Foundry will let your app use additional CPU when it's available, but only some of that CPU is guaranteed to be available to the app

"How much CPU is guaranteed to be available to the app" is its "CPU entitlement." This value scales with the amount of memory you assign to the app. Currently this is not straightforward to look for, but cloud.gov support has recommended some resources:

• Cloud Foundry video about CPU entitlement -- watch the first few minutes, at least, for a demo of how the "CPU" metric is misleading.
• CPU Entitlement blog post -- a good conceptual overview
• Using the CPU entitlement plug-in
• Cloud Foundry container metrics doc -- note that we get the absolute_entitlement and absolute_usage metrics, not cpu_entitlement
• Cloud.gov knowledge base article about metrics -- Includes instructions for accessing a dashboard with graphs