6000字 | 深入理解 Ribbon 的架構原理

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"大家好，我是悟空。","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":"本篇主要內容如下：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/87/87b525cb1bfae24c3a5028acc004b916.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"前言","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"今天我們來看下微服務中非常重要的一個組件：","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"Ribbon","attrs":{}}],"attrs":{}},{"type":"text","text":"。它作爲負載均衡器在分佈式網絡中扮演着非常重要的角色。","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":"在介紹 Ribbon 之前，不得不說下負載均衡這個比較偏僻的名詞。爲什麼說它偏僻了，因爲在面試中，聊得最多的是消息隊列和緩存來提高系統的性能，支持高併發，很少有人會問負載均衡，究其原因，負載均衡的組件選擇和搭建一般都是運維團隊或者架構師去做的，開發人員確實很少接觸到。不過沒關係，我們不止有 CRUD，還要有架構思維。","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":"簡單來說，負載均衡就是將網絡流量（負載）分攤到不同的網絡服務器（可以平均分配，也可以不平均），系統就可以實現服務的水平橫向擴展。","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":"strong","attrs":{}}],"text":"那麼如果讓你設計一個負載均衡組件，你會怎麼設計？","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":"我們需要考慮這幾個因素：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如何獲取及同步服務器列表？涉及到與註冊中心的交互。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如何將負載進行分攤？涉及到分攤策略。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如何將客戶端請求進行攔截然後選擇服務器進行轉發？涉及到請求攔截。","attrs":{}}]}]}],"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":"抱着這幾個問題，我們從負載均衡的原理 + Ribbon 的架構來學習如何設計一個負載均衡器，相信會帶給你一些啓發。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"一、負載均衡","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"1.1 概念","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上次我在這篇文章中詳細講解了何爲高可用，裏面沒有涉及到負載均衡機制，其實負載均衡也是高可用網絡的關鍵組件。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/7e/7e522817ac1afd3e2d125f02acbad5cb.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"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":"兩個基本點：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"選擇哪個服務器來處理客戶端請求。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"將客戶端請求轉發出去。","attrs":{}}]}]}],"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":"一個核心原理：通過硬件或軟件的方式維護一個服務列表清單。當用戶發送請求時，會將請求發送給負載均衡器，然後根據負載均衡算法從可用的服務列表中選出一臺服務器的地址，將請求進行轉發，完成負載功能。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"1.2 負載均衡的特性","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/e4/e43e156d130edbbbbecb0ef6a1e1ca21.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"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":"strong","attrs":{}}],"text":"高性能","attrs":{}},{"type":"text","text":"：可根據不同的分配規則自動將流量進行分攤。","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":"strong","attrs":{}}],"text":"可擴展性","attrs":{}},{"type":"text","text":"：可以很方便增加集羣中設備或鏈路的數量。","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":"strong","attrs":{}}],"text":"高可靠性","attrs":{}},{"type":"text","text":"：系統中某個設備或鏈路發生故障，不會導致服務中斷。","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":"strong","attrs":{}}],"text":"易配置性","attrs":{}},{"type":"text","text":"：配置和維護方便。","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":"strong","attrs":{}}],"text":"透明性","attrs":{}},{"type":"text","text":"：用戶感知不到如何進行負載均衡的，也不用關心負載均衡。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"1.3 負載均衡分類","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"負載均衡技術可以按照軟件或硬件進行分類，也可以按照服務器列表存放的位置劃分爲服務端負載和客戶端負載均衡。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ad/ad01f595e24edae99ddf6c1a43e71459.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"1.3.1 硬件負載均衡","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"F5 就是常見的硬件負載均衡產品。","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":"優點：性能穩定，具備很多軟件負載均衡不具備的功能，如應用交換，會話交換、狀態監控等。","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":"缺點：設備價格昂貴、配置冗餘，沒有軟件負載均衡靈活，不能滿足定製化需求。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"1.3.2 軟件負載均衡","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Nginx：性能好，可以負載超過 1W。工作在網絡的7層之上，可以針對http應用做一些分流的策略。Nginx也可作爲靜態網頁和圖片服務器。Nginx僅能支持http、https和Email協議。","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":"LVS（Linux Virtual Server）：是一個虛擬服務器集羣系統，採用 IP 地址均衡技術和內容請求分發技術實現負載均衡。接近硬件設備的網絡吞吐和連接負載能力。抗負載能力強、是工作在網絡4層之上僅作分發之用。自身有完整的雙機熱備方案，如LVS+Keepalived。軟件本身不支持正則表達式處理，不能做動靜分離。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"1.3.3 服務端負載均衡","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Nginx 和 F5 都可以劃分到服務端的負載均衡裏面，後端的服務器地址列表是存儲在後端服務器中或者存在專門的 Nginx 服務器或 F5 上。","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":"服務器的地址列表的來源是通過註冊中心或者手動配置的方式來的。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"1.3.4 客戶端負載均衡","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"終於輪到 Ribbon 登場了，它屬於客戶端負載均衡器，客戶端自己維護一份服務器的地址列表。這個維護的工作就是由 Ribbon 來乾的。","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":"Ribbon 會從 Eureka Server 讀取服務信息列表，存儲在 Ribbon 中。如果服務器宕機了，Ribbon 會從列表剔除宕機的服務器信息。","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":"Ribbon 有多種負載均衡算法，我們可以自行設定規則從而請求到指定的服務器。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"二、 均衡策略","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面已經介紹了各種負載均衡分類，接下來我們來看下這些負載均衡器如何通過負載均衡策略來選擇服務器處理客戶端請求。","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":"常見的均衡策略如下。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"2.1 輪循均衡（Round 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隨機均衡（Random）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"原理：將請求隨機分配給不同的服務器。","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":"場景：適合客戶端請求的頻率比較隨機的場景。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"2.4 響應速度均衡（Response 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中負載均衡組件。","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":"Ribbon 主要有五大功能組件：ServerList、Rule、Ping、ServerListFilter、ServerListUpdater。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/12/1218aa6fb7242881bcff27a6b03d446b.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"3.1 負載均衡器 LoadBalancer","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"用於管理負載均衡的組件。初始化的時候通過加載 YMAL 配置文件創建出來的。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"3.2 服務列表 ServerList","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"ServerList 主要用來獲取所有服務的地址信息，並存到本地。","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":"根據獲取服務信息的方式不同，又分爲靜態存儲和動態存儲。","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":"靜態存儲：從配置文件中獲取服務節點列表並存儲到本地。","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":"動態存儲：從註冊中心獲取服務節點列表並存儲到本地","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"3.3 服務列表過濾 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的分區規則對服務實例進行過濾。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"比較服務實例的通信失敗數和併發連接數來剔除不夠健康的實例。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"根據所屬區域過濾出同區域的服務實例。","attrs":{}}]}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"3.4 服務列表更新 ServerListUpdater","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"服務列表更新就是 Ribbon 會從註冊中心獲取最新的註冊表信息。是由這個接口 ServerListUpdater 定義的更新操作。而它有兩個實現類，也就是有兩種更新方式：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通過定時任務進行更新。由這個實現類 PollingServerListUpdater 做到的。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"利用 Eureka 的事件監聽器來更新。由這個實現類 EurekaNotificationServerListUpdater 做到的。","attrs":{}}]}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"3.5 心跳檢測 Ping","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"IPing 接口類用來檢測哪些服務可用。如果不可用了，就剔除這些服務。","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":"實現類主要有這幾個：PingUrl、PingConstant、NoOpPing、DummyPing、NIWSDiscoveryPing。","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":"心跳檢測策略對象 IPingStrategy，默認實現是輪詢檢測。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"3.6 負載均衡策略 Rule","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Ribbon 的負載均衡策略和之前講過的負載均衡策略有部分相同，先來個全面的圖，看下 Ribbon 有哪幾種負載均衡策略。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/b1/b1409154ebc64ac653522241e9baa234.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"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":"再來看下 Ribbon 源碼中關於均衡策略的 UML 類圖。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ea/ea8d993917183ef28feab1ad81d0b1c4.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"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":"由圖可以看到，主要由以下幾種均衡策略：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"線性輪詢均衡","attrs":{}},{"type":"text","text":" （RoundRobinRule）：輪流依次請求不同的服務器。優點是無需記錄當前所有連接的狀態，無狀態調度。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"可用服務過濾負載均衡","attrs":{}},{"type":"text","text":"（AvailabilityFilteringRule）：過濾多次訪問故障而處於斷路器狀態的服務，還有過濾併發連接數量超過閾值的服務，然後對剩餘的服務列表按照輪詢策略進行訪問。默認情況下，如果最近三次連接均失敗，則認爲該服務實例斷路。然後保持 30s 後進入迴路關閉狀態，如果此時仍然連接失敗，那麼等待進入關閉狀態的時間會隨着失敗次數的增加呈指數級增長。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"加權響應時間負載均衡","attrs":{}},{"type":"text","text":"（WeightedResponseTimeRule）：爲每個服務按響應時長自動分配權重，響應時間越長，權重越低，被選中的概率越低。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"區域感知負載均衡","attrs":{}},{"type":"text","text":"（ZoneAvoidanceRule）：更傾向於選擇發出調用的服務所在的託管區域內的服務，降低延遲，節省成本。Spring Cloud Ribbon 中默認的策略。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"重試負載均衡","attrs":{}},{"type":"text","text":"（RetryRule)：通過輪詢均衡策略選擇一個服務器，如果請求失敗或響應超時，可以選擇重試當前服務節點，也可以選擇其他節點。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"高可用","attrs":{}},{"type":"text","text":"（Best Available)：忽略請求失敗的服務器，儘量找併發比較低的服務器。注意：這種會給服務器集羣帶來成倍的壓力。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"隨機負載均衡","attrs":{}},{"type":"text","text":"（RandomRule）：隨機選擇服務器。適合併發比較大的場景。","attrs":{}}]}]}],"attrs":{}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"四、 Ribbon 攔截請求的原理","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本文最開始提出了一個問題：負載均衡器如何將客戶端請求進行攔截然後選擇服務器進行轉發？","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":"結合上面介紹的 Ribbon 核心組件，我們可以畫一張原理圖來梳理下 Ribbon 攔截請求的原理：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/dd/dd4e11136936527d83ca5f575a26a445.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"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":"第一步：Ribbon 攔截所有標註","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"@loadBalance","attrs":{}}],"attrs":{}},{"type":"text","text":"註解的 RestTemplate。RestTemplate 是用來發送 HTTP 請求的。","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":"第二步：將 Ribbon 默認的攔截器 LoadBalancerInterceptor 添加到 RestTemplate 的執行邏輯中，當 RestTemplate 每次發送 HTTP 請求時，都會被 Ribbon 攔截。","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":"第三步：攔截後，Ribbon 會創建一個 ILoadBalancer 實例。","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":"第四步：ILoadBalancer 實例會使用 RibbonClientConfiguration 完成自動配置。就會配置好 IRule，IPing，ServerList。","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":"第五步：Ribbon 會從服務列表中選擇一個服務，將請求轉發給這個服務。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"五、Ribbon 初始化的原理","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"當我們去剖析 Ribbon 源碼的時候，需要找到一個突破口，而 @LoadBalanced 註解就是一個比較好的入口。","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":"先來一張 Ribbon 初始化的流程圖：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/58/5859a8c2b839ec29974221c9a66f277a.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"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":"添加註解的代碼如下所示：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"@LoadBalanced\n@Bean\npublic RestTemplate getRestTemplate() {\n return new RestTemplate();\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":"第一步：Ribbon 有一個自動配置類 LoadBalancerAutoConfiguration，SpringBoot 加載自動配置類，就會去初始化 Ribbon。","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":"第二步：當我們給 RestTemplate 或者 AsyncRestTemplate 添加註解後，Ribbon 初始化時會收集加了 @LoadBalanced 註解的 RestTemplate 和 AsyncRestTemplate ，把它們放到一個 List 裏面。","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":"第三步：然後 Ribbon 裏面的 RestTemplateCustomizer 會給每個 RestTemplate 進行定製化，也就是加上了攔截器：LoadBalancerInterceptor。","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":"第四步：從 Eureka 註冊中心獲取服務列表，然後存到 Ribbon 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":"第五步：加載 YMAL 配置文件，配置好負載均衡配置，創建一個 ILoadbalancer 實例。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"六、Ribbon 同步服務列表原理","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Ribbon 首次從 Eureka 獲取全量註冊表後，就會隔一定時間獲取註冊表。原理圖如下：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/93/93185dc9da2fbd66590b7be0a23ddad3.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"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":"之前我們提到過 Ribbon 的核心組件 ServerListUpdater，用來同步註冊表的，它有一個實現類 PollingServerListUpdater ，專門用來做定時同步的。默認1s 後執行一個 Runnable 線程，後面就是每隔 30s 執行 Runnable 線程。這個 Runnable 線程就是去獲取 Eureka 註冊表的。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"七、Eureka 心跳檢測的原理","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們知道 Eureka 註冊中心是通過心跳檢測機制來判斷服務是否可用的，如果不可用，可能會把這個服務摘除。爲什麼是可能呢？因爲 Eureka 有自我保護機制，如果達到自我保護機制的閥值，後續就不會自動摘除。","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":"這裏我們可以再複習下 Eureka 的自我保護機制和服務摘除機制。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"Eureka 心跳機制","attrs":{}},{"type":"text","text":"：每個服務每隔 30s 自動向 Eureka Server 發送一次心跳，Eureka Server 更新這個服務的最後心跳時間。如果 180 s 內（版本1.7.2 bug ）未收到心跳，則任務服務故障了。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"Eureka 自我保護機制","attrs":{}},{"type":"text","text":"：如果上一分鐘實際的心跳次數，比我們期望的心跳次數要小，就會觸發自我保護機制，不會摘除任何實例。期望的心跳次數：服務實例數量 * 2 * 0.85。","attrs":{}}]}]},{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"Eureka 服務摘除機制","attrs":{}},{"type":"text","text":"：不是一次性將服務實例摘除，每次最多隨機摘除 15%。如果摘除不完，1 分鐘之後再摘除。","attrs":{}}]}]}],"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":"說完 Eureka 的心跳機制和服務摘除機制後，我們來看下 Ribbon 的心跳機制。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"八、Ribbon 心跳檢測的原理","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Ribbon 的心跳檢測原理和 Eureka 還不一樣，","attrs":{}},{"type":"text","marks":[{"type":"strong","attrs":{}}],"text":"Ribbon 不是通過每個服務向 Ribbon 發送心跳或者 Ribbon 給每個服務發送心跳來檢測服務是否存活的","attrs":{}},{"type":"text","text":"。","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":"先來一張圖看下 Ribbon 的心跳檢測機制：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/bb/bbc288b0e40adfbf421cc9aa051e49d3.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"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":"Ribbon 心跳檢測原理：對自己本地緩存的 Server List 進行遍歷，看下每個服務的狀態是不是 UP 的。具體的代碼就是 isAlive 方法。","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":"核心代碼：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"isAlive = status.equals(InstanceStatus.UP);\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":"那麼多久檢測一次呢？","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":"默認每隔 30s 執行以下 PingTask 調度任務，對每個服務執行 isAlive 方法，判斷下狀態。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"九、Ribbon 常用配置項","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"9.1 禁用 Eureka","attrs":{}}]},{"type":"codeblock","attrs":{"lang":"properties"},"content":[{"type":"text","text":"# 禁用 Eureka\nribbon.eureka.enabled=false\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":"服務註冊列表默認是從 Eureka 獲取到的，如果不想使用 Eureka，可以禁用掉。然後我們需要手動配置服務列表。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"9.2 配置服務列表","attrs":{}}]},{"type":"codeblock","attrs":{"lang":"properties"},"content":[{"type":"text","text":"ribbon-config-passjava.ribbon.listOfServers=localhost:8081,localhost:8083\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":"這個配置是針對具體服務的，前綴就是服務名稱，配置完之後就可以和之前一樣使用服務名稱來調用接口了。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"9.3 其他配置項","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/21/21c3db938e5f5e37dfdb3a91bbf563b1.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"十、總結","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本篇深入講解了 Spring Cloud 微服務中 負載均衡組件 Ribbon 架構原理，分爲幾大塊：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","attrs":{"listStyle":null},"content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Ribbon 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PassJava》項目，公衆號：","attrs":{}},{"type":"codeinline","content":[{"type":"text","text":"悟空聊架構","attrs":{}}],"attrs":{}},{"type":"text","text":"。本文已收錄至 ","attrs":{}},{"type":"link","attrs":{"href":"https://link.juejin.cn/?target=http%3A%2F%2Fwww.passjava.cn","title":"https://link.juejin.cn/?target=http%3A%2F%2Fwww.passjava.cn","type":null},"content":[{"type":"text","text":"www.passjava.cn","attrs":{}}]}]}]}