42圖揭祕，「後端技術學些啥」

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」，對於我們應屆生小白，難免會覺得比較陌生，因爲在學校確實比較少遇見這些所謂高大上的東西，那麼今天就帶着學習的態度和大家分享這些看似可以裝逼可以飛的帶逼格的關鍵詞吧。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/20/20d6a54a67a101033f47c3714e240c9e.png","alt":"大綱","title":null,"style":null,"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":"--------"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"1 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」足矣，但是爲了面試考慮，我們又不得不找點類似"},{"type":"text","marks":[{"type":"strong"}],"text":"秒殺系統"},{"type":"text","text":"作爲我們簡歷的支撐項目(即使已經爛大街)。那麼先問你第一個問題，爲什麼就採用了"},{"type":"text","marks":[{"type":"strong"}],"text":"分佈式"},{"type":"text","text":"的方案落地這個項目？"}]}]},{"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":"當一個人或者幾十個使用你的系統，哎呀我去，請求秒回，效果倍棒，於是乎簡歷砰砰寫上卻多麼牛X，當面試官就會問你你這項目做了啥，測試過沒，併發量如何，性能如何？你就....."}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/60/6087cd1789144e3195116f2e1afd4d1f.gif","alt":"在這裏插入圖片描述","title":null,"style":null,"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}},{"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":"當訪問系統的用戶越來越多，可是我們的系統資源有限，所以需要更多的 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和*"},{"type":"text","marks":[{"type":"italic"}],"text":"內存"},{"type":"text","text":"*去處理用戶的計算請求，當然也就要求更大的"},{"type":"text","marks":[{"type":"strong"}],"text":"網絡帶寬"},{"type":"text","text":"去處理數據的傳輸，也需要更多的磁盤空間存儲數據。資源不夠，消耗過度，服務器崩潰，系統也就不幹活了，那麼在這樣的情況怎麼處理？"}]},{"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":"strong"}],"text":"垂直伸縮"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"縱向生長。通過提升"},{"type":"text","marks":[{"type":"strong"}],"text":"單臺"},{"type":"text","text":"服務器的"},{"type":"text","marks":[{"type":"strong"}],"text":"計算處理"},{"type":"text","text":"能力來抵抗更大的請求訪問量。比如使用更快頻率的CPU，更快的網卡，塞更多的磁盤等。其實這樣的處理方式在電信，銀行等企業比較常見，讓摩托車變爲小汽車，更強大的計算機，處理能力也就越強，但是對於運維而言也就越來越複雜。那真的就這樣花錢買設備就完事了？"}]}]},{"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":"當然不，單臺服務器的計算處理能力是有限的，而且也會嚴重受到計算機硬件水平的制約。"}]},{"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":"strong"}],"text":"水平伸縮"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"一臺機器處理不過來，我就用多臺"},{"type":"text","marks":[{"type":"strong"}],"text":"廉價"},{"type":"text","text":"的機器合併同時處理，人多力量大嘛，通過多臺服務器構成分佈式集羣從而提升系統的整體處理能力。這裏說到了分佈式，那我們看看分佈式的成長過程"}]}]},{"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":"記住一句話："},{"type":"text","marks":[{"type":"strong"}],"text":"系統的技術架構是需求所驅動"}]},{"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","text":"最初的"},{"type":"text","marks":[{"type":"strong"}],"text":"單體系統"},{"type":"text","text":"，只需要部分用戶訪問，"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" "}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/71/712cf0f9d49513529cf4cd2ff4d03dd8.png","alt":"單體結構","title":null,"style":null,"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":"做系統的原因當然是有需求，有價值，可賺錢。隨着使用系統的用戶越來越多，這時候關注的人越來越多，單臺服務器扛不住了，關注的人覺得響應真慢，沒啥意思，就開始吐槽，但是這一吐槽，導致用戶更多，畢竟大家都愛喫瓜。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/98/987fee677dadac6c14ea5b4fd154473f.gif","alt":"來自網絡喫瓜","title":null,"style":null,"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}},{"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":"這樣下去不得不進行系統的升級，將"},{"type":"text","marks":[{"type":"strong"}],"text":"數據庫和應用"},{"type":"text","text":"分離。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/9a/9a21bca20d84338968f486f035886f77.png","alt":"數據庫應用分離","title":null,"style":null,"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":"這樣子，咋們將數據庫和應用程序分離後，部署在不同的服務器中，從1臺服務器變爲多臺服務器，處理響應更快，內容也夠幹，訪問的用戶呈"},{"type":"text","marks":[{"type":"strong"}],"text":"指數增長"},{"type":"text","text":"，這多臺服務器都有點扛不住了，怎麼辦？"}]},{"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":"加一個"},{"type":"text","marks":[{"type":"strong"}],"text":"緩存"},{"type":"text","text":"吧，我們不每次從數據庫中讀取數據，而將應用程序需要的數據暫存在"},{"type":"text","marks":[{"type":"strong"}],"text":"緩衝"},{"type":"text","text":"中。緩存呢，又分爲"},{"type":"text","marks":[{"type":"strong"}],"text":"本地緩存"},{"type":"text","text":"和*"},{"type":"text","marks":[{"type":"italic"}],"text":"分佈式的緩存"},{"type":"text","text":"*。分佈式緩存，顧名思義，使用多臺服務器構成集羣，存儲更多的數據並提供緩存服務，從而提升緩存的能力。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 加了緩存哪些好處？"}]}]},{"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","text":"應用程序不再直接訪問數據庫，提升訪問效率。因爲緩存內容在內存中，不用每次連接存放磁盤中的數據庫，"}]}]}]},{"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":"系統越來越火，於是考慮將應用服務器也作爲"},{"type":"text","marks":[{"type":"strong"}],"text":"集羣"},{"type":"text","text":"。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/90/90707e0d4f5fef980ce2938969acc635.png","alt":"集羣","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":"2 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HTTPS 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id from users where username='Mike';"}]}]},{"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":"如果是惡意攻擊，提交的HTTP請求如下"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"http://www.a.com?username=Mike';drop table users;--"}]}]},{"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":"此時最終生成的SQL是"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Select id from users where username='Mike';drop table users;--';"}]}]},{"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":"查詢完就直接給刪除表了。怎麼防護？比較常用的解決方案是使用PrepareStaement預編譯，先將SQL交給數據庫生成執行計劃，後面hack不管提交什麼字符串也只能交給這個執行計劃執行，不會生成新的SQL，也就不會被攻擊啦。"}]},{"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":"XSS攻擊"}]},{"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":"跨站點腳本攻擊，攻擊者通過構造惡意的瀏覽器腳本文件，使其在其他用戶的瀏覽器運行進而進行攻擊。假設小A將含有惡意腳本的請求給360服務器，服務器將惡意的腳本存儲在本地的數據庫，當其他正常用戶通過這個服務器瀏覽信息的時候，服務器就會讀取數據庫中含有惡意腳本的數據並呈現給用戶，在用戶正常使用瀏覽器的時候達到攻擊的目的。"}]},{"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","marks":[{"type":"strong"}],"text":"防禦："}]},{"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":"比較常見的是在入口處對危險的請求比如drop table等進行攔截，設置一個Web應用防火牆將危險隔離。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/bc/bc487762c7365443a1b452dde2f67b02.png","alt":"安全防禦","title":null,"style":null,"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}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"10 大數據"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其實在上面提到的分佈式中就有涉及大數據相關知識。無外乎是數據量越來越大，我們如何儘可能使用較低的成本存儲更多的數據，更公司企業帶來更好的利潤。上面說過分佈式緩存，負載均衡等技術，其共同特點是如何抵抗高併發的壓力，而這裏的大數據技術主要談論的是如何滿足大規模的計算。"}]}]},{"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":"通過對數據的分析，進而發掘海量數據中的價值，這裏的數據包含數據庫數據，日誌信息，用戶行爲數據等等。那麼這麼多不同類型的數據，怎麼去存儲呢"}]},{"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":"strong"}],"text":"分佈式文件存儲 HDFS 架構"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如何將數以萬計的服務器組成統一的文件存儲系統？其中使用Namenode服務器作爲控制塊，負責元數據的管理(記錄文件名，訪問權限，數據存儲地址等)，而真正的文件存儲在DataNode中。"}]}]},{"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":"Mapreduce"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"大量的數據存儲下來的目的是通過相應的算法進行數據分析，獲得通過深度學習/機器學習進行預測，從而獲取有效的價值，這麼大的文件，我們不可能將HDFS當做普通的文件，從文件中讀取數據然後計算，這樣子不知道算到何時何地。"}]}]},{"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":"大數據處理經典的處理框架即MapReduce，分爲Map和Reduce兩個階段，其中一個Map過程是將每個服務器上啓動Map進程，計算後輸出一個集合。reduce過程，MapReduce在每個服務器上啓動多個reduce進程，然後將所有的map輸出的集合進行shuffle操作，什麼是shuffle操作呢，即是將相同的ekey發送到同一個reduce進程，在reduce中完成數據關聯的操作。"}]},{"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":"下面以WordCount統計所有數據中相同的詞頻數據爲例，詳細看看Map和Reduce的過程。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/22/2279bba0970ebab6a073c3f9168e12c0.png","alt":"wordcoun計算過程","title":null,"style":null,"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}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在這個例子中，通過對value中的1組成的列表，reduce對這些1進行求和操作從而得到每個單詞的詞頻。代碼實現如下"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"java"},"content":[{"type":"text","text":"public class WordCount {\n // Mapper四個參數：第一個Object表示輸入key的類型；第二個Text表示輸入value的類型；第三個Text表示表示輸出鍵的類型；第四個IntWritable表示輸出值的類型。map這裏的輸出是指輸出到reduce \n public static class doMapper extends Mapper