Frontend Learning Book

Feature Toggles (often also refered to as Feature Flags) are a powerful technique, allowing teams to modify system behavior without changing code. 允许团队不用修改代码而来改变系统的功能行为。

“Feature Toggling” is a set of patterns which can help a team to deliver new functionality to users rapidly but safely.

https://martinfowler.com/articles/feature-toggles.html

Types of Feature Toggles

• Release Toggle: When developing code that is not ready for consumption and has a high risk of breaking the application. 发布型：出现在生产环境上，用于开放或者隐藏部分特性功能的toggle；
• Experimental Toggle: When performing multivariate testing (e.g. AB Testing). 体验型：即A/B testing，用于区分A、B方案的实际使用情况；
• Operation Toggle: When rolling out a new feature with unclear performance impact. 操作型：提供给操作员工的一系列特殊操作。比如遭到DOS攻击时可以关掉网络端口。
• Permission Toggle: Used in cases of dogfooding, alpha and beta programs. 权限型：使得部分指定范围内的用户可以体验到新特性功能，而并不是面向全部用户。

Why Feature Toggle

Feature Toggle allows us to decouple Release from Deployment

• Deployed: A technical concern that applies in the domain of the team and means the functionality is introduced in Production.
• Released: A business term that defines functionality being available to an end-user. Deployed doesn’t necessarily mean Released.

每两个周发布一次生产版本，但是同时又需要去维护一个很多个月才能进行发布的特性分支。feature toggle可以保障团队成员们在开发主线(mainline)上的工作不受到未完全实现的特性分支的影响.

https://www.jianshu.com/p/6931b0abc956

When do we remove it

• When experiment is over (We can’t be doing one experiment forever)
• When release is approved (e.g. Mock Closing ended)

Introduce purpose-fit implementation separately for Permission Toggle and Authorization Service.

Feature Toggle Lifecycle

• When setting up feature toggle, it will be disabled by default. Any users that want to see the feature needs to opt in.
• When feature is ready to be released to general users, we can enable the feature by default.
• At the end of the lifecycle, the feature toggle would be removed in the next release.

Disabled by default -> Enabled for developers -> Enabled for QA -> Enabled for Product Team -> Enabled for UAT users -> Enabled for general users -> Remove Feature Toggle

Maintain Toggle Config file

基础思路：存在一个配置文件，配置文件里定义了许多的toggle，这些toggle都是待发布的特性功能。这一些toggle定义了哪一些features需要呈现，哪些并不需要。

• Toggle feature (on/off) by updating Toggle Config File for each environments.
• This config file will be maintained in source code repository for version control.
• CICD pipeline will be set up differently from existing Frontend code build pipeline.
• Config file will be maintained in a different bucket / different folder from existing site assets.
• Raise a Jira ticket and assign to dev team to update config file for lower environments (dev, stage, preprod); or raise a support ticket.

• Raise a support ticket to update config file for production site.

• Edit config file in code repository (Bitbucket)

• Push edited config file into Bitbucket
• Changes in Bitbucket triggers CICD pipeline
• CICD pipeline pushes edited config file into S3 bucket
• Config file is served via Lambda & API Gateway

// toggleConfig.json
{
   "defaults":{
      "feature1": false
   },
   "groups":{
      "developer": {
         "feature1": true
      }
   },
   "users":{
      "user1":{
         "feature1": false
      },
   }
}
// toggleGroupConfig.json
{
    "developer":[ "user1" ],
    "productOwner": [ "user2" ]
}