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kyverno/docs/dev/feature-flags
Aditya Kumar bdeb172a7e
Minor changes in dev docs (#11266)
Signed-off-by: Aditya Kumar <aditya.kumar60@infosys.com>
2024-09-30 13:54:02 +00:00
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README.md Minor changes in dev docs (#11266) 2024-09-30 13:54:02 +00:00

Feature Flags Guidelines

Introduction

Feature flags, also known as feature toggles, are a software development technique that allows developers to turn features on and off in a production environment without requiring a new deployment.

There are several ways to enable/disable features in Golang:

  1. Feature Toggles: It provides a simple way to enable/disable features based on environment variables and/or command line arguments
  2. Container arguments

Feature Flags

The toggle package exists in pkg/toggle can be used to define and manage a feature toggle for a new feature in Kyverno. Let's say we need to introduce a new feature toggle to enable/disable deferred loading. We can do it as follows:

  1. Define a flag name, description, environment variable and a default value for this new feature in the toggle package:

    EnableDeferredLoadingFlagName    = "enableDeferredLoading"
    EnableDeferredLoadingDescription = "enable deferred loading of context variables"
    enableDeferredLoadingEnvVar      = "FLAG_ENABLE_DEFERRED_LOADING"
    defaultEnableDeferredLoading     = true
    
  2. Create a new toggle for the new feature using the newToggle method which takes both default value and environment variable as arguments:

    EnableDeferredLoading    = newToggle(defaultEnableDeferredLoading, enableDeferredLoadingEnvVar)
    

    At this point, we have an instance of toggle which will be used later to call toggle.enabled() of the feature toggle to execute code conditionally.

  3. Add a new method EnableDeferredLoading() bool in Toggles Interface at pkg/toggle/context.go to call the enabled method. It will be used later in Kyverno controllers:

    type Toggles interface {
        EnableDeferredLoading() bool
    }
    
    func (defaultToggles) EnableDeferredLoading() bool {
        return EnableDeferredLoading.enabled()
    }
    
  4. In the controller, we can use it as follows:

    flag.Func(toggle.EnableDeferredLoadingFlagName, toggle.EnableDeferredLoadingDescription, toggle.EnableDeferredLoading.Parse)
    

Advantages

  1. Feature toggles can be accessed globally. Its value can be checked anywhere in the code, no need to pass it as an argument among methods/functions.

  2. Users can either enable/disable the feature by setting it as an argument to the container --enableDeferredLoading=false or setting its environment variable FLAG_ENABLE_DEFERRED_LOADING=0

Container Arguments

Container arguments can be used directly in the controller. Let's say we want to add a new container flag --enable-feature, we can do it as follows:

  1. Create a variable for this new flag:
var(
    enableFeature bool
)
  1. Define a bool flag with specified name, default value, and usage:
flagset.BoolVar(&enableFeature, "enable-feature", true, "Set this flag to 'false' to ....")