{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"},{"type":"strong"}],"text":"微服系列文章"}]},{"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1篇： "},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/83386f6d764984f3b64b760fb","title":""},"content":[{"type":"text","text":"“四個維度” 講明白什麼是微服務！"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第2篇： "},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/e4c9866b723b7c4f9cc272050","title":""},"content":[{"type":"text","text":"微服務涉及的技術生態有哪些？"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第3篇： "},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/13a6973621381b27bbcd9ab45","title":""},"content":[{"type":"text","text":" 微服務-爲什麼要有服務發現與註冊？"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第4篇： "},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/c6139a5776e139d1b76b2e856","title":""},"content":[{"type":"text","text":" 萬字長文，助你吃透Eureka服務發現機制！"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"前言"}]},{"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":"在前面幾篇系列文章中，我們對"},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/83386f6d764984f3b64b760fb","title":""},"content":[{"type":"text","text":"微服務的基本概念"}]},{"type":"text","text":"、"},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/e4c9866b723b7c4f9cc272050","title":""},"content":[{"type":"text","text":"微服務的技術生態"}]},{"type":"text","text":"等，做了簡單的闡述。對於分佈式系統或微服務，服務發現是最基礎、最核心、最不可缺的能力。然而許多人對服務發現有一種說不清，道不明，似懂非懂的感覺。"}]},{"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":"這都無可厚非，畢竟服務發現涉及到分佈式相關的知識，而分佈式的知識浩如煙海，晦澀難懂，如：分佈式協議、分佈式事務，資源協調，Zookeeper等，光這一堆的概念就讓人望而卻步。我們知道，學習一門技術，如果不深入理解背後要解決的問題與設計原理，就很難做到靈活運用，觸類旁通。"}]},{"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":"這篇文章我們就從服務發現的基本概念入手，再結合Eureka的具體實現，來深入分析服務發現背後要解決的問題與設計原理。"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"這不僅是我們閱讀這個系列文章，學習微服務，學習分佈式系統的必經之路，同時很多的設計理論也可以爲我們學習其他技術（如：Hadoop,區塊鏈等）打下堅實的基礎。"}]},{"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"}],"text":"文章比較長，大約有1萬3千多字，建議大家打開目錄進行閱讀，現在我們就以下面四個問題爲線索，來全面解析Eureka服務發現的原理機制。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"1）如何理解服務發現這一概念？"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"2）服務發現要解決的問題是什麼？"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"3）Eureka是如何設計服務發現？"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"4）Eureka如何保證高可用與數據一致？"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"一、"},{"type":"text","text":"如何理解服務發現這一概念？"}]},{"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":"一個概念往往是對某一個領域，某個問題的高度概括，要理解服務發現這個概念，我們 從分佈式系統說起，這裏我不想引用百度詞條或專業的術語給分佈式系統下一個定義，這容易讓人產生困惑，我引用一句更通俗易懂的古語來對分佈式系統做個比喻："}]},{"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":"#D46B08","name":"brown"}}],"text":" “當一頭牛拉不動車的時候，不要試圖去尋找一頭更強壯的牛，而是要用兩頭牛來拉” "}]},{"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":"因此，從狹義上來講分佈式系統可以理解爲："},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"由諸多應用程序協同合作來完成任務的一種工作模式系統"},{"type":"text","text":"。這裏的任務可能是一個商品的下單操作，可能是一個超大集合的排序計算，可能是存儲一個超大的文件，也可能是繪製團戰遊戲的實時畫面。總之，這個任務由於各種條件限制，很難由單個程序獨立完成，而需要由多個程序一起協同完成，這種工作模式我們用計算機語言總結有4個特徵："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"1）協同工作的各個程序運行在由區域、機房、機櫃，交換機、網線連接的計算機上；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"2）程序之間通過一次或者多次遠程調用或數據傳遞來完成某項任務；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"3）程序可能會奔潰，硬盤可能會損壞，CPU可能會跑滿，網絡可能會抖動；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"4）任務成功與否由多個程序共同決定，一個程序失敗，可能整個任務都失敗；"}]}]}]},{"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":"看了以上4個特徵，是不是覺得分佈式系統的工作模式有些不靠譜，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"這種工作模式太複雜、充滿不確定性，非常脆弱"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"。"},{"type":"text","text":"這有點像馬戲團小丑的雜技表演，腳下踩着獨輪車，頭上頂着碗，雙手還不停的拋着皮球，這種表演很脆弱，只要任何一個小地方出現閃失，比如某個球沒接住掉到地上，那表演就算失敗。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f6/f69897918d8d9bc942a8798a72ec8336.jpeg","alt":null,"title":"","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"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":"分佈式系統也是如此，所有環境，所有程序只要某個環節出現一點問題，都會影響整個任務的執行結果。面對這種不確定性與複雜性，計算機科學家們無論在學術理論還是工程實踐方面，想了很多辦法也沉澱了很多成果，包括："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"抽象提煉問題，如互斥性問題，冪等性問題，拜占庭將軍問題等；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"總結昇華定律，如CAP理論，BASE理論等；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"解決設計算法，如Paxos算法，ZAB算法，分佈式哈希算法等；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"規範定義概念，如服務發現，分佈式事務，負載均衡，配置中心等；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"開發工程工具，如Zookeeper，Eureka，GTS，Apollo等；"}]}]}]},{"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":"#D46B08","name":"brown"}}],"text":"因此我們看到，服務發現在整個分佈式生態中的位置，它是整個分佈式生態中一個十分重要的概念"},{"type":"text","text":"，這個概念代表着分佈式中某一個具體的問題域，圍繞這一概念還涉及分佈式生態中其他很多知識，如：CAP的理論基礎，ZAB的算法思想，Zookeepr或Eureka的工程工具等等。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"二、服務發現要解決的問題是什麼？"}]},{"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":"上面我們說到，服務發現是爲解決分佈式環境中某問題域而產生的一個概念，那具體是針對哪些問題域，具體要解決哪些問題呢？"}]},{"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":"服務發現要解決的第一個問題就是--"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"解耦、屏蔽程序之間 IP與端口的依賴。 "},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"在分佈式系統工作特徵中我們說過“程序之間通過一次或者多次遠程調用或數據傳遞來完成某項任務\""},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}},{"type":"strong"}],"text":"，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"因此，調用程序方首先要知道被調用程序在網絡中的標識，我們知道在計算機網絡里程序的標識是用"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"IP+端口"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"來實現，但這種方式存在兩個問題。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"IP與端口沒有任何特殊含義不便於理解、不便於記憶；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"當程序部署的IP與端口改變，程序的調用者也要同步修改；"}]}]}]},{"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":"而通過服務發現，可以將服務之間IP與端口的依賴轉化爲服務名的依賴，服務名可以根據具體微服務業務特徵來命名，因此，屏蔽、解耦服務之間IP與端口的依賴是服務發現要解決的第一個問題。"}]},{"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":"服務發現要解決的另一個問題是--"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"動態管理程序的狀態"},{"type":"text","text":"，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"user"}}],"text":"在分佈式系統工作特徵中我們說過，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"“程序可能會奔潰，硬盤可能會損壞，CPU可能會跑滿，網絡可能會抖動"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}},{"type":"strong"}],"text":"\"，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"因此，在分佈式環境中程序的狀態是隨時發生變化的，而且從某種程度上來說這種變化不可預測，誰也不知道下一秒某個程序會不會掛掉，一旦某個程序出問題，調用者還未得到通知的話，可能會發生多米勒骨牌式的連鎖反應。"}]},{"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":"#000000","name":"black"}}],"text":"而服務發現可以對服務的狀態進行實時管理，當程序狀態發生改變時，可以第一時間通知到程序的使用者，我們可以從如下兩個方面去理解這種管理能力。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"首先，程序要能彼此知曉對方的信息與狀態；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"其次，當對方信息與狀態發生變化時要能及時知曉；"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 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{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"},{"type":"strong"}],"text":"微服系列文章"}]},{"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1篇： "},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/83386f6d764984f3b64b760fb","title":""},"content":[{"type":"text","text":"“四個維度” 講明白什麼是微服務！"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第2篇： "},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/e4c9866b723b7c4f9cc272050","title":""},"content":[{"type":"text","text":"微服務涉及的技術生態有哪些？"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第3篇： "},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/13a6973621381b27bbcd9ab45","title":""},"content":[{"type":"text","text":" 微服務-爲什麼要有服務發現與註冊？"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第4篇： "},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/c6139a5776e139d1b76b2e856","title":""},"content":[{"type":"text","text":" 萬字長文，助你吃透Eureka服務發現機制！"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"前言"}]},{"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":"在前面幾篇系列文章中，我們對"},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/83386f6d764984f3b64b760fb","title":""},"content":[{"type":"text","text":"微服務的基本概念"}]},{"type":"text","text":"、"},{"type":"link","attrs":{"href":"https://xie.infoq.cn/article/e4c9866b723b7c4f9cc272050","title":""},"content":[{"type":"text","text":"微服務的技術生態"}]},{"type":"text","text":"等，做了簡單的闡述。對於分佈式系統或微服務，服務發現是最基礎、最核心、最不可缺的能力。然而許多人對服務發現有一種說不清，道不明，似懂非懂的感覺。"}]},{"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":"這都無可厚非，畢竟服務發現涉及到分佈式相關的知識，而分佈式的知識浩如煙海，晦澀難懂，如：分佈式協議、分佈式事務，資源協調，Zookeeper等，光這一堆的概念就讓人望而卻步。我們知道，學習一門技術，如果不深入理解背後要解決的問題與設計原理，就很難做到靈活運用，觸類旁通。"}]},{"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":"這篇文章我們就從服務發現的基本概念入手，再結合Eureka的具體實現，來深入分析服務發現背後要解決的問題與設計原理。"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"這不僅是我們閱讀這個系列文章，學習微服務，學習分佈式系統的必經之路，同時很多的設計理論也可以爲我們學習其他技術（如：Hadoop,區塊鏈等）打下堅實的基礎。"}]},{"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"}],"text":"文章比較長，大約有1萬3千多字，建議大家打開目錄進行閱讀，現在我們就以下面四個問題爲線索，來全面解析Eureka服務發現的原理機制。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"1）如何理解服務發現這一概念？"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"2）服務發現要解決的問題是什麼？"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"3）Eureka是如何設計服務發現？"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"4）Eureka如何保證高可用與數據一致？"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"一、"},{"type":"text","text":"如何理解服務發現這一概念？"}]},{"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":"一個概念往往是對某一個領域，某個問題的高度概括，要理解服務發現這個概念，我們 從分佈式系統說起，這裏我不想引用百度詞條或專業的術語給分佈式系統下一個定義，這容易讓人產生困惑，我引用一句更通俗易懂的古語來對分佈式系統做個比喻："}]},{"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":"#D46B08","name":"brown"}}],"text":" “當一頭牛拉不動車的時候，不要試圖去尋找一頭更強壯的牛，而是要用兩頭牛來拉” "}]},{"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":"因此，從狹義上來講分佈式系統可以理解爲："},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"由諸多應用程序協同合作來完成任務的一種工作模式系統"},{"type":"text","text":"。這裏的任務可能是一個商品的下單操作，可能是一個超大集合的排序計算，可能是存儲一個超大的文件，也可能是繪製團戰遊戲的實時畫面。總之，這個任務由於各種條件限制，很難由單個程序獨立完成，而需要由多個程序一起協同完成，這種工作模式我們用計算機語言總結有4個特徵："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"1）協同工作的各個程序運行在由區域、機房、機櫃，交換機、網線連接的計算機上；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"2）程序之間通過一次或者多次遠程調用或數據傳遞來完成某項任務；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"3）程序可能會奔潰，硬盤可能會損壞，CPU可能會跑滿，網絡可能會抖動；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"4）任務成功與否由多個程序共同決定，一個程序失敗，可能整個任務都失敗；"}]}]}]},{"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":"看了以上4個特徵，是不是覺得分佈式系統的工作模式有些不靠譜，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"這種工作模式太複雜、充滿不確定性，非常脆弱"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"。"},{"type":"text","text":"這有點像馬戲團小丑的雜技表演，腳下踩着獨輪車，頭上頂着碗，雙手還不停的拋着皮球，這種表演很脆弱，只要任何一個小地方出現閃失，比如某個球沒接住掉到地上，那表演就算失敗。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f6/f69897918d8d9bc942a8798a72ec8336.jpeg","alt":null,"title":"","style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"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":"分佈式系統也是如此，所有環境，所有程序只要某個環節出現一點問題，都會影響整個任務的執行結果。面對這種不確定性與複雜性，計算機科學家們無論在學術理論還是工程實踐方面，想了很多辦法也沉澱了很多成果，包括："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"抽象提煉問題，如互斥性問題，冪等性問題，拜占庭將軍問題等；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"總結昇華定律，如CAP理論，BASE理論等；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"解決設計算法，如Paxos算法，ZAB算法，分佈式哈希算法等；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"規範定義概念，如服務發現，分佈式事務，負載均衡，配置中心等；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"開發工程工具，如Zookeeper，Eureka，GTS，Apollo等；"}]}]}]},{"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":"#D46B08","name":"brown"}}],"text":"因此我們看到，服務發現在整個分佈式生態中的位置，它是整個分佈式生態中一個十分重要的概念"},{"type":"text","text":"，這個概念代表着分佈式中某一個具體的問題域，圍繞這一概念還涉及分佈式生態中其他很多知識，如：CAP的理論基礎，ZAB的算法思想，Zookeepr或Eureka的工程工具等等。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"二、服務發現要解決的問題是什麼？"}]},{"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":"上面我們說到，服務發現是爲解決分佈式環境中某問題域而產生的一個概念，那具體是針對哪些問題域，具體要解決哪些問題呢？"}]},{"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":"服務發現要解決的第一個問題就是--"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"解耦、屏蔽程序之間 IP與端口的依賴。 "},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"在分佈式系統工作特徵中我們說過“程序之間通過一次或者多次遠程調用或數據傳遞來完成某項任務\""},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}},{"type":"strong"}],"text":"，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"因此，調用程序方首先要知道被調用程序在網絡中的標識，我們知道在計算機網絡里程序的標識是用"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"IP+端口"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"來實現，但這種方式存在兩個問題。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"IP與端口沒有任何特殊含義不便於理解、不便於記憶；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"當程序部署的IP與端口改變，程序的調用者也要同步修改；"}]}]}]},{"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":"而通過服務發現，可以將服務之間IP與端口的依賴轉化爲服務名的依賴，服務名可以根據具體微服務業務特徵來命名，因此，屏蔽、解耦服務之間IP與端口的依賴是服務發現要解決的第一個問題。"}]},{"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":"服務發現要解決的另一個問題是--"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"動態管理程序的狀態"},{"type":"text","text":"，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"user"}}],"text":"在分佈式系統工作特徵中我們說過，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"“程序可能會奔潰，硬盤可能會損壞，CPU可能會跑滿，網絡可能會抖動"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}},{"type":"strong"}],"text":"\"，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"因此，在分佈式環境中程序的狀態是隨時發生變化的，而且從某種程度上來說這種變化不可預測，誰也不知道下一秒某個程序會不會掛掉，一旦某個程序出問題，調用者還未得到通知的話，可能會發生多米勒骨牌式的連鎖反應。"}]},{"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":"#000000","name":"black"}}],"text":"而服務發現可以對服務的狀態進行實時管理，當程序狀態發生改變時，可以第一時間通知到程序的使用者，我們可以從如下兩個方面去理解這種管理能力。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"首先，程序要能彼此知曉對方的信息與狀態；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"其次，當對方信息與狀態發生變化時要能及時知曉；"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" "}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"三、Eureka是如何設計服務發現的？"}]},{"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":"前面我們對服務發現的概念與要解決的問題做了簡單的介紹，這都是爲理解服務發現的設計原理做的鋪墊。下面我們就以Eureka服務發現爲例，來分析一下服務發現是如何設計的。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"1、引用一個統一管理中心"}]},{"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":"服務發現的目標是要抽象程序標識並對程序狀態進行動態管理。一旦涉及到管理，我們第一個想到的是什麼？集權、集中、統一，設置一個機構等等。Eureka也是如此，要管理這些程序，先要有一個統一的管理中心，這個統一的管理中心就是"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"--註冊中心。"}]},{"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":"因此，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"註冊中心可以認爲是Eureka的大腦，肩負着Eureka的各項管理，協調職能"},{"type":"text","text":"。"}]},{"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":"使用統一的管理中心這一設計思想，在分佈式架構中幾乎無處不在，如Hadoop，Zookeeper等等。而作爲對比的非統一中心設計思想，就是比特幣，比特幣中的節點程序除了在功能上有所區分（如錢包節點，挖礦節點）在職能上沒有任何特殊的中心節點。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"2、定義四個基礎概念"}]},{"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":"#40A9FF","name":"blue"}}],"text":"理清服務端、客戶端、生產者，消費者四個基本概念"}]},{"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":"將註冊中心作爲服務發現中的管理者是個不錯的主意。就像公司一樣，從職責上對員工進行劃分，比如：出錢的--老闆，找活幹的--產品經理，監督幹活的--項目經理，正真幹活的--程序員，背鍋的--初級程序員。"}]},{"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":"爲了理解溝通方便，服務發現對管理者與非管理者也進行了劃分，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"負責管理的註冊中心--服務端，負責具體完成任務的程序--客戶端"},{"type":"text","marks":[{"type":"italic"},{"type":"color","attrs":{"color":"#FF7021","name":"orange"}},{"type":"strong"}],"text":"，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"這就是服務器端與客戶端的概念。"}]},{"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":"通過服務端與客戶端的概念，從職責上對程序進行了區分，但是，對於具體幹活的客戶端，還有一個問題：那就是它們之間的調用關係錯綜複雜，能不能從調用關係這個維度對客戶端再進行區分呢？"}]},{"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":"答案是肯定的，因此，對於客戶端又分爲生產者，消費者的概念。例如，一個任務需要兩個程序協調合作，程序A調用程序B，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"調用方也就是程序A叫--消費者，被調用方也就是程序B叫--生產者。"}]},{"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":"#40A9FF","name":"blue"}}],"text":"生產者與消費者只是概念上的區別，它們並不是單獨的兩類程序而是一類，都屬於客戶端。一個程序是不是生產者與消費者並不是絕對的，可能是生產者，可能是消費者，也可能既是生產者也是消費者，這取決於我們看待的角度。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ef/efbe6ccc7c155a74f2a3b9b3afd2e080.png","alt":null,"title":"服務器端、客戶端、生產者、消費者","style":[{"key":"width","value":"100%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"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":"#D46B08","name":"brown"}}],"text":"服務端，客戶端、生產者、消費者這四個概念非常重要"},{"type":"text","text":"，在涉及服務發現的文章中（包括本文，網上或者相關書籍）都會被大量重複提及。我們要結合上下文去理解這些概念，否則碰到一段話就很難看懂，甚至會被誤導。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"3、抽象七個基本運行流程"}]},{"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":"理順了相關的概念之後，下面我們重點來介紹Eureka服務發現的基本運行流程，這會使我們對Eureka有一個初步的整體認識，這是理解後面更復雜內容的前提，也是進一步研究源碼的基礎。"}]},{"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":"我將Eureka基本運行流程抽象爲七個步驟，當然這七個步驟並不是嚴格的順序執行，更不是官方的說法，只是讓我們更好的理解Eureka的工作流程，這7個步驟分別如下："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"1、客戶端發起服務註冊；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"2、服務端保存信息至註冊表；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"3、客戶端定時發送心跳請求；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"4、服務端服務剔除與自我保護"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"5、客服端發送服務下線請求"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"6、客戶端獲取服務端註冊表；"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#40A9FF","name":"blue"}}],"text":"7、客戶端整合服務發現；"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ff/fff9e8edb7cdac788dd826ae91357d64.png","alt":null,"title":"Eureka整體運行流程","style":[{"key":"width","value":"100%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"1、客戶端發起服務註冊"}]},{"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":"#40A9FF","name":"blue"}}],"text":"客戶端向服務器發送請求，將自身的相關信息提交給服務端；"}]},{"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":"#000000","name":"black"}}],"text":"對於這一步驟很好理解，即當客戶端程序啓動時，先要加入到分佈式系統中，第一步就是要向服務器提供自身的信息並告訴服務端我來了。這跟婚介所有點像，你想在婚介所找對象，就得先到婚介所登記提供自己的詳細信息，只有這樣女孩子纔可能瞭解到你。在服務發現中這一過程就叫"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":" --服務註冊"},{"type":"text","marks":[{"type":"italic"},{"type":"size","attrs":{"size":12}},{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"。"}]},{"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Eureka是如何實現服務註冊這一過程的呢？"}]},{"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":"#40A9FF","name":"blue"}}],"text":"服務端提供一個對外註冊接口，用來接收客戶端的註冊請求，服務端啓動後會一直監聽這個接口，等待客戶端調用；"}]},{"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":"#40A9FF","name":"blue"}}],"text":"客戶端在啓動時，先找到服務端與自身的配置信息（分區，名稱，IP，端口等），再調用服務端的註冊接口將相關信息發送給服務端；"}]},{"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":"關於配置信息可能在客戶端程序的配置文件中，也可能在統一的配置中心，配置中心在這個系列文章中我們會詳細介紹。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/2f/2f92e49defebfd28cc87894bc53c4e9f.png","alt":null,"title":"客戶端服務註冊子流程","style":[{"key":"width","value":"100%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#000000","name":"black"}}],"text":"2、服務端保存信息至註冊表"}]},{"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":"#40A9FF","name":"blue"}}],"text":"服務端將客戶端提交的註冊信息保存至本地內存註冊表；"}]},{"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":"這一步驟很簡單，也沒有任何流程與通信。但這裏的"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"註冊表"},{"type":"text","text":"可能是Eureka中最核心，最關鍵的概念，註冊表的作用就跟數據庫一樣，不管是我們正在討論的7個基本運行流程，還有後面要說的數據同步操作等，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"brown"}}],"text":"其本質就是圍繞着對註冊表添加、更新、刪除、獲取，同步等一系列操作。"}]},{"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":"註冊表這麼重要，那註冊表到底長什麼樣，存儲了哪些數據呢？其實，"},{"type":"text","marks":[{"type":"color","attrs":{"color":"#D46B08","name":"user"}}],"text":"Eureka註冊表是一個雙字典結構的數據"},{"type":"text","text":"， 服務發現的目標是標識與管理服務的狀態，因此註冊表裏面存儲的有服務標識，服務基本信息，服務狀態等數據，如下圖所示："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/03/03da245ae372c265a31ba862a9e3adfd.png","alt":null,"title":"註冊表雙字典結構","style":[{"key":"width","value":"100%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"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":"italic"}],"text":"本篇文章，我本不打算加入任何源代碼，後面計劃是寫一篇專門對Eureka源碼分析的文章。但是，這裏要理解註冊表的雙字典結構，最高效的方式還是直接看看源碼的定義，如下代碼："}]},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"ConcurrentHashMap發表評論
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