如何在Go 服務中做鏈路追蹤

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"使用 Go 語言開發微服務的時候，需要追蹤每一個請求的訪問鏈路，這塊在 Go 中目前沒有很好的解決方案。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在 Java 中解決這個問題比較簡單，可以使用 MDC，在一個進程內共享一個請求的 RequestId。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在 Go 中實現鏈路追蹤有兩種思路：一種是在項目中使用一個全局的 map， key 是 goroutine 的唯一 Id，value 是 RequestId，另一種思路可以使用 context.Context 來實現。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面的代碼基於 gin 框架來實現。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"1. 使用全局 map 來實現","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"使用 map 方案需要在全局維護一個 map，在一個請求進來的時候，會爲每一個請求生成 RequestId，然後在每次在打印日誌的時候，從這個 Map 中通過 goid 獲取到 RequestId，打印到日誌中。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"代碼的實現很簡單：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"go"},"content":[{"type":"text","text":"var requestIdMap = make(map[int64]string) // 全局的 Map\n\nfunc main() {\n r := gin.Default()\n r.Use(Logger()) // 使用中間件\n\n r.GET(\"/index\", func(c *gin.Context) {\n Info(\"main goroutine\") // 打印日誌\n\n c.JSON(200, gin.H{\n \"message\": \"index\",\n })\n })\n r.Run()\n}\n\nfunc Logger() gin.HandlerFunc {\n return func(c *gin.Context) {\n requestIdMap[goid.Get()] = uuid.New().String() // 在日誌中間件中爲每個請求設定\n c.Next()\n }\n}\n\nfunc Info(msg string) {\n now := time.Now()\n nowStr := now.Format(\"2006-01-02 15:04:05\")\n fmt.Printf(\"%s [%s] %s\\n\", nowStr, requestIdMap[goid.Get()], msg) // 打印日誌\n}\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這樣的實現很簡單，但是問題也很多。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第一個問題就是，在 Go 程序中，一次請求可能會涉及到多個 goroutine，用這種方式很難在多個 gotoutine 之間傳遞 RequestId。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在下面的代碼中，如果新啓動了一個 goroutine，就會導致日誌中獲取不到 RequestId：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"go"},"content":[{"type":"text","text":"func main() {\n r := gin.Default()\n r.Use(Logger())\n\n r.GET(\"/index\", func(c *gin.Context) {\n Info(\"main goroutine\")\n\n go func() { // 這裏新啓動了一個一個 goroutine\n Info(\"goroutine1\")\n }()\n\n c.JSON(200, gin.H{\n \"message\": \"index\",\n })\n })\n r.Run()\n}\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"獲取 goroutine id 也不是一種常規的做法，一般要通過 hack 的方式來獲取，這種做法已經不推薦了。而且這個全局的 map 爲了併發安全，在實際的使用中，可以還需要用到鎖，在高併發的情況下必然會影響性能。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在每個請求結束的時候，還需要手動的把 requestId 從 map 中刪除，否則就會造成內存泄漏。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"總的來說，使用 map 這種方式來實現並不是很好。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"2. 使用 Context 來實現","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在上面的代碼中，我們使用一個 hack 的方式去獲取 goroutine id，這種方式早就不推薦使用，更推薦使用 Context，關於 Context 內容，可以去看我之前的文章，在這裏就不多說了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在傳遞 RequestId 的場景中，同樣也可以使用 Context 來實現，使用 Context 好處很明顯，Context 生命週期與請求相同，不需要手動銷燬。而且Context 是每個請求獨享的，也不用擔心併發安全的問題，Context 還可以在 goroutine 之間傳遞。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"使用 Context 實現的代碼如下：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"go"},"content":[{"type":"text","text":"func main() {\n r := gin.Default()\n r.Use(Logger())\n\n r.GET(\"/index\", func(c *gin.Context) {\n\n ctx, _ := c.Get(\"ctx\")\n\n Info(ctx.(context.Context) , \"main goroutine\")\n\n go func() {\n Info(ctx.(context.Context), \"goroutine1\")\n }()\n\n c.JSON(200, gin.H{\n \"message\": \"index\",\n })\n })\n r.Run()\n}\n\nfunc Logger() gin.HandlerFunc {\n return func(c *gin.Context) {\n valueCtx := context.WithValue(c.Request.Context(), \"RequestId\", uuid.New().String())\n c.Set(\"ctx\", valueCtx)\n c.Next()\n }\n}\n\nfunc Info(ctx context.Context, msg string) {\n now := time.Now()\n nowStr := now.Format(\"2006-01-02 15:04:05\")\n fmt.Printf(\"%s [%s] %s\\n\", nowStr, ctx.Value(\"RequestId\"), msg)\n}\n","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這樣在一個請求中，所有的 gotroutine 都可以獲取到同一個 RequestId，而且不用擔心內存泄漏和併發安全。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"但是使用 Context 也有個問題就是需要每次傳遞 Context，很多人還不習慣使用這種方式。其實 Go 官方早就推薦使用 Context了，通常會把 Context 作爲函數的第一個參數。如果函數使用結構體作爲參數，也可以直接把 Context 作爲結構體的一個字段。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Context 除了使用可以同來傳遞 RequestId 之外，還可以用來控制 goroutine 的生命週期，這些內容在之前的 Context 文章中詳細說明了，感興趣的可以去看看。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"3. 小結","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"獲取 goroutine id 這種方式應該被拋棄，而是應該使用 Context, Go 官方也早就推薦使用這種方式，在上文中，我們使用 Context 來傳遞 RequestId，除此之外還可以用來傳遞單個請求範圍的值，比如認證的 token 之類的，應該習慣在代碼中使用 Context。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"[1] ","attrs":{}},{"type":"link","attrs":{"href":"https://blog.golang.org/context","title":"","type":null},"content":[{"type":"text","text":"https://blog.golang.org/context","attrs":{}}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#FF7021","name":"orange"}}],"text":"文 / Rayjun","attrs":{}}]}]}