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How-to-write-flusher-plugins.md

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如何开发 Flusher 插件

Flusher 插件与外部系统进行交互，将数据发送到外部，以下将从接口定义与案例2方面指导如何开发 Flusher 插件

Flusher 接口定义

  • Init: 插件初始化接口，对于Flusher 主要作用是创建外部资源链接

  • Description： 插件描述

  • IsReady：插件系统在调用 Flush 前会调用该接口检查当前 flusher 是否仍能够处理更多数据，如果答案为否的话，它会等待一段时间再重试。

  • Flush 接口是插件系统向 flusher 插件实例提交数据的入口，用于将数据输出到外部系统。为了映射到日志服务的概念中，我们增加了三个 string 参数，它代表这个 flusher 实例所属的 project/logstore/config。详细解释请参与数据结构 与 基本结构 。

  • SetUrgent： 标识iLogtail 即将退出，将系统状态传递给具体Flusher 插件，可以供Flusher 插件自动适应系统状态，比如加快输出速率等。

  • Stop：停止Flusher 插件，比如断开与外部系统交互的链接

    type Flusher interface {
// Init called for init some system resources, like socket, mutex...
Init(Context) error

// Description returns a one-sentence description on the Input.
Description() string

// IsReady checks if flusher is ready to accept more data.
// @projectName, @logstoreName, @logstoreKey: meta of the corresponding data.
// Note: If SetUrgent is called, please make some adjustment so that IsReady
//   can return true to accept more data in time and config instance can be
//   stopped gracefully.
IsReady(projectName string, logstoreName string, logstoreKey int64) bool

// Flush flushes data to destination, such as SLS, console, file, etc.
// It is expected to return no error at most time because IsReady will be called
// before it to make sure there is space for next data.
Flush(projectName string, logstoreName string, configName string, logGroupList []*protocol.LogGroup) error

// SetUrgent indicates the flusher that it will be destroyed soon.
// @flag indicates if main program (Logtail mostly) will exit after calling this.
//
// Note: there might be more data to flush after SetUrgent is called, and if flag
//   is true, these data will be passed to flusher through IsReady/Flush before
//   program exits.
//
// Recommendation: set some state flags in this method to guide the behavior
//   of other methods.
SetUrgent(flag bool)

// Stop stops flusher and release resources.
// It is time for flusher to do cleaning jobs, includes:
// 1. Flush cached but not flushed data. For flushers that contain some kinds of
//   aggregation or buffering, it is important to flush cached out now, otherwise
//   data will lost.
// 2. Release opened resources: goroutines, file handles, connections, etc.
// 3. Maybe more, it depends.
// In a word, flusher should only have things that can be recycled by GC after this.
Stop() error
}

Flusher 开发

Flusher 的开发分为以下步骤:

  1. 创建Issue，描述开发插件功能，会有社区同学参与讨论插件开发的可行性，如果社区review 通过，请参考步骤2继续进行。
  2. 实现 Flusher 接口，这里我们使用样例模式进行介绍，详细样例请查看flusher/stdout ，你可以使用 example.json 试验此插件功能。
  3. 将插件加入全局插件定义中心, 如果仅运行于指定系统，请添加到Linux插件定义中心 或 Windows插件定义中心.
  4. 进行单测或者E2E测试，请参考如何使用单测 与 如何使用E2E测试.
  5. 使用 make lint 检查代码规范。
  6. 提交Pull Request。