# 快速迭代：如何使用 feature toggle 來開發佈署應用程式 - Aki wang Noah hsu

{%hackmd @DevOpsDay/B1cnefOI0 %}

#### 》[議程介紹](https://devopsdays.tw/2024/session-page/3098)
#### 》[填寫議程滿意度問卷｜回饋建言給辛苦的講者](https://forms.gle/66hToGrb1V7hL5gV9)

> 共筆從這開始

### Prerequisite
- Docker Engine: 23+
- Java: JDK 11+ (recommand 17)
- sdk and sample code: [line/Flagship4j](https://github.com/line/Flagship4j)

## feature toggle

因為使用多個branch做開發，有時候有些branch太早開發，但太晚merge進去，中間會有很多其他小開發完成，這樣就會產生merge conflict。
這時候就要去處理這樣的問題
但feature toggle可以有相關的解方。

### feature切換

常常button換顏色的時候要換來換去，這樣也很苦惱

## feature toggle 優勢與特色

- Invisibility
- 沒有enable的話code是看不到的
- Speed
- 加速開發週期
- 先merge什麼都沒做的source code，再merge做了一半的source code)
- Experimentation
- 體驗性，例如切換不同顏色的button，也可以設定權限)
- 可以做很多切換體驗不同的效果
- Safety
- 程式碼安全，可以快速關閉跟開啟功能
- Live Update
- 可以快速的real time將流量導過去，讓影響降低到最低。

## [toggle type](https://martinfowler.com/articles/feature-toggles.html)

- release toggles
- 開發到一半的功能先關閉，開發完之後再出現
- 大概幾週的時間去處理
- ops toggle
- 某些功能比較複雜，可能會造成程式的 crash，先關掉也不會造成影響
- 可能會留在上面比較長的時間，驗證更改前後的狀況，比較效能上面的問題。
- experiment toggles
- 將user去分群給予不同畫面去體驗處理。
- permission toggles
- 今天可能去驗證身份，給予不同的權限去看不同的介面

## 是第二個好方法，最終要去盡量避免
> "feature toggle is second best solution. the best solution is to find a way to gradually intergrate without feature branches and feature toggles" by Martin Fowler

## [Flagship4j](https://github.com/line/Flagship4j)
LINE Taiwan 開發的，已經開源出來了

## open feature
有三個特點：
1. one SDK, any backend
- 今天開 interface 出來，
- 統一一個介面，去使用 feature toggle
2. support your favorite tools
3. speak your language
- 多種語言

## openFlagr
AB testing，用go來撰寫的。performance非常的好。

### Prerequisite
- Docker Engine: 23+
- Java: JDK 11+ (recommand 17)
- sdk and sample code: [line/Flagship4j](https://github.com/line/Flagship4j)

###### tags: `DevOpsDays Taipei 2024`
第一個是未完成Code 的 Merege 問題
第二個是新需求的Adopt，新舊功能都留著

Invisibility
Speed
Experimentation
Safety
Live Update

Realse Toggle ： 承上

Ops Toggles : 流量大有另外函數

Permission Toggles ： 權限控制

Experiment Toggles ： 使用者體驗

### Toggle remove
toggle測試結束的時候最終要拿掉，不然會累積太多很難處理，會把code跟toggle feature一起拿掉。

### testing
基本上會希望非開發人員可以去處理，QA或是project owner可以去改變跟測試

### Demo step

1. 下載專案
sdk and sample code: [line/Flagship4j](https://github.com/line/Flagship4j)

2. install library

./gradlew publishToMavenLocal

3. start a new spring boot application (with web and lombok)
or use the example in the downloaded project

implementation "com.linecorp.flagship4j:flagship4j-openfeature-spring-boot-starter:0.1.40-SNAPSHOT"

4. create a controller with openfeature client
5.

5. create flag setting on the openflagr UI (release toggle)

6. trun toggle to permission togggle (constraints by `role`)

7. add `MutableContext` as a third parameter when call client.getBooleanValue()

### throw Exception

@RestController
@RequiredArgsConstructor
public class LayoutController {

    private final Client flagrClient;

    @GetMapping("/layouts/product")
    public ResponseEntity<?> getLayoutProduct() {
        return ResponseEntity.ok(buildLayoutProduct());
    }

    private Map<?, ?> buildLayoutProduct() {
        throw new UnsupportedOperationException("Not implemented yet");
    }

}

### On / Off with not found

@RestController
@RequiredArgsConstructor
public class LayoutController {

    private final Client flagrClient;

    @GetMapping("/layouts/product")
    public ResponseEntity<?> getLayoutProduct() {
        if (flagrClient.getBooleanValue("layout-prdocut-enabled", false)) {
            return ResponseEntity.ok(buildLayoutProduct());
        }

        return ResponseEntity.notFound().build();
    }

    private Map<?, ?> buildLayoutProduct() {
        return Map.of("btnBuyColor", "blue", "btnBuyRadius", "8px", "btnBuyPos", "page");
    }

}

### WhiteList

@RestController
@RequiredArgsConstructor
public class LayoutController {

    private final Client flagrClient;

    @GetMapping("/layouts/product")
    public ResponseEntity<?> getLayoutProduct(@RequestHeader(name = "x-user-name", required = false) String userName) {
        MutableContext context = new MutableContext();
        if (userName != null && userName.equals("aki")) {
            context.add("entityContext", Structure.mapToStructure(Map.of("role", "ROLE_QA")));
        }

        if (flagrClient.getBooleanValue("layout-prdocut-enabled", false, context)) {
            return ResponseEntity.ok(buildLayoutProduct());
        }

        return ResponseEntity.notFound().build();

    }

    private Map<?, ?> buildLayoutProduct() {
        return Map.of("btnBuyColor", "blue", "btnBuyRadius", "8px", "btnBuyPos", "page");
    }

}

### A/B Testing

@RestController
@RequiredArgsConstructor
public class LayoutController {

    private final Client flagrClient;

    @GetMapping("/layouts/product")
    public ResponseEntity<?> getLayoutProduct(@RequestHeader(name = "x-user-name", required = false) String userName) {
        MutableContext context = new MutableContext();
        if (userName != null && userName.equals("aki")) {
            context.add("entityContext", Structure.mapToStructure(Map.of("role", "ROLE_QA")));
        }

        if (flagrClient.getBooleanValue("layout-prdocut-enabled", false, context)) {
            String theme = flagrClient.getStringValue("layout-product-theme", "themeA", new MutableContext(userName));

            switch (theme) {
                case "themeA":
                    return ResponseEntity.ok(buildThemeALayoutProduct());
                case "themeB":
                    return ResponseEntity.ok(buildThemeBLayoutProduct());
                default:
                    return ResponseEntity.notFound().build();
            }
        }

        return ResponseEntity.notFound().build();

    }

    private Map<?, ?> buildThemeALayoutProduct() {
        return Map.of("btnBuyColor", "blue", "btnBuyRadius", "8px", "btnBuyPos", "page");
    }

    private Map<?, ?> buildThemeBLayoutProduct() {
        return Map.of("btnBuyColor", "green", "btnBuyRadius", "0px", "btnBuyPos", "bottomNav");
    }

}