cpu-entitlement-plugin

README

Cloud Foundry CPU Entitlement Plugin (EXPERIMENTAL)

Examine the CPU usage of Cloud Foundry applications, relative to their CPU entitlement.

Installation

Get the binary URL for your platform

$ cf install-plugin $URL

Usage

Collect CPU metrics for existing Cloud Foundry applications by running:

$ cf cpu-entitlement $APP_NAME

Note: Getting information about previous spikes requires cf-deployment version >v12.1.0!

Building

Note: Dependencies for cpu-entitlement-plugin are managed using go modules. You do not need to clone this repo to your GOPATH. Please ensure you have go version >=1.11 installed.

To install the latest version:

$ cd cpu-entitlement-plugin
$ make install

# for more options run: make help

What is the cpu-entitlement-plugin?

The CPU entitlement plugin lets you see how much CPU your application is using compared to its entitlement. Your CPU entitlement is calculated based on the requested memory limit of your application: for example, a 128MB application is entitled to use twice as much CPU as a 64MB application. The exact mapping from memory to CPU is determined by the platform operator.

This plugin allows Cloud Foundry application developers to make better decisions about scaling applications and initial resource allocation of applications.

Will my application be throttled?

Current versions of Cloud Foundry allow applications to use more CPU than they are entitled to if CPU time is available at that moment, regardless of how the application has behaved in the past. This behaviour will change in the future; applications will still be allowed to temporarily exceed their entitlement but preference will be given to those applications that have been using less than their entitlement over a rolling window of time. Applications will never be forced below their entitlement.

For operators

An application entitled to 25% of the system CPU and using 25% of it is using all the CPU it's entitled to and probably needs to be scaled up to keep up with its workload. cf app will report a usage of 25%, while this plugin will report a usage of 100%. On the other hand, an application entitled to 50% of the system CPU and using 25% of it is idling 50% of the time: cf app will still report a 25% usage, while this plugin will report a usage of 50%.

Eventually we intend to use the entitlement usage metrics to automatically make decisions about application CPU throttling. Operators can use this plugin to visualise which applications will be throttled when the new behaviour is introduced. The metrics currently reported by Cloud Foundry (e.g. by running cf app) can't provide this information, as they represent absolute CPU usage and are dependant on the CPU usage of all the other applications running on the same cell. For example, an application averaging at 130% usage of its entitlement may be throttled to allow other applications to temporarily exceed their entitlement.

Operators may wish to over-commit or under-commit on the number of CPU shares available to applications for entitlement. This configuration and the outcomes are documented in the garden BOSH release.