Nacos-技術專題-配置中心實現

{"type":"doc","content":[{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"什麼是 Nacos"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" "},{"type":"codeinline","content":[{"type":"text","text":"Nacos"}]},{"type":"text","text":"是阿里發起的開源項目，地址："},{"type":"link","attrs":{"href":"https://link.zhihu.com/?target=https%3A//github.com/alibaba/nacos","title":null},"content":[{"type":"text","text":"https://github.com/alibaba/nacos"}]},{"type":"text","text":"。"},{"type":"codeinline","content":[{"type":"text","text":"Nacos"}]},{"type":"text","text":"主要提供兩種服務，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"一是配置中心，支持配置註冊、變更下發、層級管理等，意義是不停機就可以動態刷新服務內部的配置項；"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#9254DE","name":"purple"}},{"type":"strong"}],"text":"二是作爲命名服務，提供服務的註冊和發現功能，通常用於在 "},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#9254DE","name":"purple"}},{"type":"strong"}],"text":"RPC"}],"marks":[{"type":"color","attrs":{"color":"#9254DE","name":"purple"}},{"type":"strong"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#9254DE","name":"purple"}},{"type":"strong"}],"text":" 框的 "},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#9254DE","name":"purple"}},{"type":"strong"}],"text":"Client"}],"marks":[{"type":"color","attrs":{"color":"#9254DE","name":"purple"}},{"type":"strong"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#9254DE","name":"purple"}},{"type":"strong"}],"text":" 和 "},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#9254DE","name":"purple"}},{"type":"strong"}],"text":"Server"}],"marks":[{"type":"color","attrs":{"color":"#9254DE","name":"purple"}},{"type":"strong"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#9254DE","name":"purple"}},{"type":"strong"}],"text":" 中間充當媒介，還附帶有健康監測、負載均衡等功能。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 本文聚焦於 "},{"type":"codeinline","content":[{"type":"text","text":"Nacos"}]},{"type":"text","text":" 的第一塊功能，即配置中心的實現。先敘述一個配置中心通常需要哪些組成部分，再結合 "},{"type":"codeinline","content":[{"type":"text","text":"Nacos 1.1.4"}]},{"type":"text","text":" 的源碼，探究一下這些設計是如何反映在源碼上的。"}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"配置中心的架構"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 配置中心本身並不複雜，前提是你先將 "},{"type":"codeinline","content":[{"type":"text","text":"CAP"}]},{"type":"text","text":" 的取捨問題晾在一邊的話。"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"配置中心最基礎的功能就是存儲一個鍵值對，用戶發佈一個配置（"},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"configKey"}],"marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"），然後客戶端獲取這個配置項（"},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"configValue"}],"marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"）；進階的功能就是當某個配置項發生變更時，將變更告知客戶端刷新舊值。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" "},{"type":"text","marks":[{"type":"strong"}],"text":"下方的架構圖，簡要描述了一個配置中心的大致架構，用戶可以通過管理平臺發佈配置，通過 "},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"strong"}],"text":"HTTP"}],"marks":[{"type":"strong"}]},{"type":"text","marks":[{"type":"strong"}],"text":" 調用將配置註冊到服務端，服務端將之保存在 "},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"MySQL"}],"marks":[{"type":"strong"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":" "},{"type":"text","marks":[{"type":"strong"}],"text":"等持久化存儲引擎中；"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":" 用戶通過客戶端 "},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"SDK"}],"marks":[{"type":"strong"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":" "},{"type":"text","marks":[{"type":"strong"}],"text":"訪問服務端的配置，同時建立 "},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"HTTP"}],"marks":[{"type":"strong"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":" "},{"type":"text","marks":[{"type":"strong"}],"text":"的長輪詢監聽配置項變更，同時爲了減輕服務端壓力和保證容災特性，配置項拉取到客戶端之後會保存一份快照在本地文件中，SDK 優先讀取文件裏的內容。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 例如配置"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"分層設計，權限校驗，客戶端長輪詢的間隔設置"},{"type":"text","text":"，服務端每次查詢都需要訪問 "},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"MySQL"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":" "},{"type":"text","text":"麼，配置變更是主動推送還是等定時輪詢觸發等，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"還有就是運維高可用方面的工作（私以爲這個是配置中心的精華），例如節點跨地域部署，網絡分區時配置如何保證可寫可推送變更等。"},{"type":"text","marks":[{"type":"strong"}],"text":"真正實現一個高質量的配置中心，還是需要長時間打磨的。"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/7c/7c2bac31e8bfcde6e89f547a316cb1be.jpeg","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Nacos 使用示例"}]},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下文涉及的源碼均基於 Nacos 1.1.4 版本"}]}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"官方代碼示例"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 先看一下官方文檔中對於 "},{"type":"codeinline","content":[{"type":"text","text":"Nacos"}]},{"type":"text","text":" 的 "},{"type":"codeinline","content":[{"type":"text","text":"API"}]},{"type":"text","text":" 使用的示例代碼，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 第一步是傳遞配置，新建 "},{"type":"codeinline","content":[{"type":"text","text":"ConfigService"}]},{"type":"text","text":" 實例，第二步可以通過相應的接口獲取配置和註冊配置監聽器。使用方式非常簡單易懂，不再贅述。"}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"try {\n // 傳遞配置\n String serverAddr = \"{serverAddr}\";\n String dataId = \"{dataId}\";\n String group = \"{group}\";\n Properties properties = new Properties();\n properties.put(\"serverAddr\", serverAddr);\n // 新建 configService\n ConfigService configService = NacosFactory.createConfigService(properties);\n String content = configService.getConfig(dataId, group, 5000);\n System.out.println(content);\n // 註冊監聽器\n configService.addListener(dataId, group, new Listener() {\n @Override\n public void receiveConfigInfo(String configInfo) {\n System.out.println(\"recieve1:\" + configInfo);\n }\n @Override\n public Executor getExecutor() {\n return null;\n }\n \t});\n\t} catch (NacosException e) {\n // TODO -generated catch block\n e.printStackTrace();\n\t}"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"Properties 解讀"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 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"},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"dataId"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":" 可以理解爲用戶自定義的配置健，"},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"group"}],"marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":" 可以理解爲配置分組名稱，這個屬於配置層級設計的概念。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":" "},{"type":"text","marks":[{"type":"strong"}],"text":"簡單來說，配置中心會通過層次設計，來支持不同的分區，以此區分不同的環境、不同的分組、甚至不同的開發者，滿足在開發過程中灰度發佈、測試等需求。"},{"type":"text","text":"因此怎樣設計都可以，只要有含義就好，例如下圖也不是不可以。"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/28/28d3bcbac84f1945497b1f1a44bbf061.jpeg","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Nacos 客戶端解析"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"獲取配置"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 獲取配置的主要方法是 "},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"NacosConfigService"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":" "},{"type":"text","text":"類的 "},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"getConfigInner"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":" "},{"type":"text","text":"方法，通常情況下該方法直接從本地文件中取得配置的值，如果本地文件不存在或者內容爲空，則再通過 "},{"type":"codeinline","content":[{"type":"text","text":"HTTP GET"}]},{"type":"text","text":" 方法從遠端拉取配置，並保存到本地快照中。"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/2a/2a3c7cd6d6638a1b89a234f916d41985.jpeg","alt":null,"title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 當通過 "},{"type":"codeinline","content":[{"type":"text","text":"HTTP"}]},{"type":"text","text":" 獲取遠端配置時，"},{"type":"codeinline","content":[{"type":"text","text":"Nacos"}]},{"type":"text","text":" 提供了兩種熔斷策略，一是超時時間，二是最大重試次數，默認重試三次。"}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"註冊監聽器"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 配置中心客戶端對某個配置項註冊監聽器是很常見的需求，達到在配置項變更時候執行回調的功能。"}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"iconfig.addListener(dataId, group, ml);\niconfig.getConfigAndSignListener(dataId, group, 1000, ml);"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" "},{"type":"codeinline","content":[{"type":"text","text":"Nacos"}]},{"type":"text","text":" 可以通過以上方式註冊監聽器，它們內部的實現均是調用 "},{"type":"codeinline","content":[{"type":"text","text":"ClientWorker"}]},{"type":"text","text":" 類的 "},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"addCacheDataIfAbsent"}]},{"type":"text","text":"。其中 "},{"type":"codeinline","content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":"CacheData"}]},{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}},{"type":"strong"}],"text":" "},{"type":"text","text":"是一個維護配置項和其下注冊的所有監聽器的實例，私以爲這個名字取得並不好，不容易理解。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 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