基于.NET的大型Web站點StackOverflow架構分析

發布時間: 2011-03-04 17:03 閱讀: 3859 次推薦: 1 [收藏]

原文鏈接：Stack Overflow Architecture Update - Now At 95 Million Page Views A Month

編譯/博客園

Stack Overflow網址：http://stackoverflow.com/

當前訪問量：每月9500PV（每天300多萬PV）

當前Alexa排名：149

所用.NET技術：C#、Visual Studio 2010 Team Suite、ASP.NET 4、ASP.NET MVC 3、Razor、LINQ to SQL+raw SQL

下面是英文原文：

A lot has happened since my first article on the Stack Overflow Architecture(2009-8-5). Contrary to the theme of that last article, which lavished attention on Stack Overflow's dedication to a scale-up strategy, Stack Overflow has both grown up and out in the last few years.

自從2009年8月發布了第一篇關于“Stack Overflow 架構”方面的文章，Stack Overflow已經發生了很大的變化。那篇文章更多關注的是Stack Overflow如何解決網站的擴展性(scale-up)問題，而經過幾年的發展，Stack Overflow已經長大成人，成長為了大型網站。

Stack Overflow has grown up by more then doubling in size to over 16 million users and multiplying its number of page views nearly 6 times to 95 million page views a month.

現在與2009年相比，Stack Overflow每月獨立訪問用戶翻了一倍，超過1600萬；每月PV翻了近6倍，達到9500萬。

Stack Overflow has grown out by expanding into the Stack Exchange Network, which includes Stack Overflow, Server Fault, and Super User for a grand total of 43 different sites. That's a lot of fruitful multiplying going on.

Stack Overflow新增了很多站點，比如Server Fault, Super User等，共有43個不同站點組成了Stack Exchange Network，可謂碩果累累，迅猛增長。

What hasn't changed is Stack Overflow's openness about what they are doing. And that's what prompted this update. A recent series of posts talks a lot about how they've been handling their growth: Stack Exchange’s Architecture in Bullet Points, Stack Overflow’s New York Data Center, Designing For Scalability of Management and Fault Tolerance, Stack Overflow Search — Now 81% Less, Stack Overflow Network Configuration, Does StackOverflow use caching and if so, how?, Which tools and technologies build the Stack Exchange Network?.

Stack Overflow的變化翻天覆地，而不變的是他們開放的心態，所以才有了這篇架構分享的文章。最近，他們寫了一系列文章分享他們如何應對這樣的快速增長。

Some of the more obvious differences across time are:
穿越時空，我們來看看有哪些明顯的變化？

Just More. More users, more page views, more datacenters, more sites, more developers, more operating systems, more databases, more machines. Just a lot more of more.
更多：更多的用戶，更多的PV，更多的數據中心，更多的站點，更多的開發者，更多的操作系統，更多的數據庫，更多的服務器...
Linux. Stack Overflow was known for their Windows stack, now they are using a lot more Linux machines for HAProxy, Redis, Bacula, Nagios, logs, and routers. All support functions seem to be handled by Linux, which has required the development of parallel release processes.
Linux：Stack Overflow因使用Windows系統而著稱，現在他們使用越來越多的Linux服務器，比如HAProxy(負載均衡), Redis(NoSQL數據庫), Bacula(數據備份系統), Nagios(遠程監控軟件), 日志, 路由器都運行于Linux系統，幾乎所有需要并行處理的功能都是由Linux處理(這句話的翻譯可能不準確)。
Fault Tolerance. Stack Overflow is now being served by two different switches on two different internet connections, they've added redundant machines, and some functions have moved to a second datacenter.
容錯：Stack Overflow使用了兩條不同的互聯網線路，增加了更多的冗余服務器，將一些網站服務運行于第二個數據中心。
NoSQL. Redis is now used as a caching layer for the entire network. There wasn't a separate caching tier before so this a big change, as is using a NoSQL database on Linux.
NoSQL：Redis作為整個網站的緩存層。這是一個巨大的改變，以前并沒有將緩存作為一個獨立的層分離出來。Redis運行于Linux。

Unfortunately, I couldn't find any coverage on some of the open questions I had last time, like how they were going to deal with multi-tenancy across so many diffrent properties, but there's still plenty to learn from. Here's a roll up a few different sources:

遺憾的是，一些我關注的問題并沒有從中找到答案，比如面對這么多不同的系統，如何解決多租戶的問題（Multi-tenancy 是一種軟件體系結構，在這種體系結構中軟件運行在 software as a service 服務商的服務器上，服務于多個客戶組織即 tenant）。但是，從中我們依然可以學到很多。下面是收集的一些數據列表：

The Stats

95 Million Page Views a Month
800 HTTP requests a second
180 DNS requests a second
55 Megabits per second
16 Million Users - Traffic to Stack Overflow grew 131% in 2010, to 16.6 million global monthly uniques.

Data Centers

1 Rack with Peak Internet in OR (Hosts our chat and Data Explorer)
2 Racks with Peer 1 in NY (Hosts the rest of the Stack Exchange Network)

Hardware

10 Dell R610 IIS web servers (3 dedicated to Stack Overflow):
- 1x Intel Xeon Processor E5640 @ 2.66 GHz Quad Core with 8 threads
- 16 GB RAM
- Windows Server 2008 R2

2 Dell R710 database servers:
- 2x Intel Xeon Processor X5680 @ 3.33 GHz
- 64 GB RAM
- 8 spindles
- SQL Server 2008 R2

2 Dell R610 HAProxy servers:
- 1x Intel Xeon Processor E5640 @ 2.66 GHz
- 4 GB RAM
- Ubuntu Server

2 Dell R610 Redis servers:
- 2x Intel Xeon Processor E5640 @ 2.66 GHz
- 16 GB RAM
- CentOS

1 Dell R610 Linux backup server running Bacula:
- 1x Intel Xeon Processor E5640 @ 2.66 GHz
- 32 GB RAM

1 Dell R610 Linux management server for Nagios and logs:
- 1x Intel Xeon Processor E5640 @ 2.66 GHz
- 32 GB RAM

2 Dell R610 VMWare ESXi domain controllers:
- 1x Intel Xeon Processor E5640 @ 2.66 GHz
- 16 GB RAM

2 Linux routers
5 Dell Power Connect switches

Dev Tools

C#: Language
Visual Studio 2010 Team Suite: IDE
Microsoft ASP.NET (version 4.0): Framework
ASP.NET MVC 3: Web Framework
Razor: View Engine
jQuery 1.4.2: Browser Framework:
LINQ to SQL, some raw SQL: Data Access Layer
Mercurial and Kiln: Source Control（分布式版本控制系統）
Beyond Compare 3: Compare Tool（文件比較工具）

Software and Technologies Used

Stack Overflow uses a WISC stack via BizSpark
Windows Server 2008 R2 x64: Operating System
SQL Server 2008 R2 running Microsoft Windows Server 2008 Enterprise Edition x64: Database
Ubuntu Server
CentOS
IIS 7.0: Web Server
HAProxy: for load balancing（高性能的負載TCP/HTTP均衡器）
Redis: used as the distributed caching layer.（作為分布式緩存層的NoSQL數據庫）
CruiseControl.NET: for builds and automated deployment（.NET平臺的持續集成工具）
Lucene.NET: for search
Bacula: for backups（開源的數據備份系統）
Nagios: (with n2rrd and drraw plugins) for monitoring（監視系統運行狀態和網絡信息的遠程監控軟件）
Splunk: for logs（日志分析工具）
SQL Monitor: from Red Gate - for SQL Server monitoring
Bind: for DNS
Rovio: a little robot (a real robot) allowing remote developers to visit the office “virtually.”
Pingdom: an external monitor and alert service.（網站監控服務及網站速度測試工具）

External Bits

Code that is not included as part of the development tools:

reCAPTCHA（用于驗證碼驗證，已被Google收購）
DotNetOpenId（.NET 平臺上的 OpenID 實現方案）
WMD - Now developed as open source. See github network graph （輕量級所見即所得編輯器）
Prettify（代碼高亮顯示）
Google Analytics
Cruise Control .NET
HAProxy（負載均衡）
Cacti（網絡流量監測圖形分析工具）
MarkdownSharp（Markdown文本處理器的C#實現）
Flot（基于JQuery的純JavaScript實現的繪圖庫）
Nginx（反向代理服務器）
Kiln（分布式版本控制系統）
CDN: none, all static content is served off the sstatic.net, which is a fast, cookieless domain intended for static content delivered to the Stack Exchange family of websites.
（沒有使用CDN，用一個專門的域名sstatic.net傳遞所有的靜態內容）

Developers and System Administrators

14 Developers
2 System Administrators

Content

License: Creative Commons Attribution-Share Alike 2.5 Generic
Standards: OpenSearch, Atom
Host: PEAK Internet

More Architecture and Lessons Learned

HAProxy is used instead of Windows NLB because HAProxy is cheap, easy, free, works great as a 512MB VM “device” on a network via Hyper-V. It also works in front of the boxes so it’s completely transparent to them, and easier to troubleshoot as a different networking layer instead of being intermixed with all your windows configuration.
用HAProxy取代了Windows NLB，HAProxy成本更低，更易于使用，通過Hyper-V可以很好地運行于512M內存的虛擬機。它工作于服務器群的最前端，對所有的服務器都透明。相比于原來混雜在一起的Windows配置，它運行于一個獨立的網絡層，更易于維護與故障處理。
A CDN is not used because even “cheap” CDNs like Amazon one are very expensive relative to the bandwidth they get bundled into their existing host’s plan. The least they could pay is $1k/month based on Amazon’s CDN rates and their bandwidth usage.
沒有使用CDN，即使使用像Amazon那樣與主機空間捆綁在一起的看起來“便宜”的CDN，實際的費用也是很高的，至少需要1000美元/月。
Backup is to disk for fast retrieval and to tape for historical archiving.
備份方案有兩種，一種用于快速恢復的磁盤備份，一種用于歷史數據存檔的磁帶備份。
Full Text Search in SQL Server is very badly integrated, buggy, deeply incompetent, so they went to Lucene.
SQL Server的全文索引是非常差勁的，所以他們用Lucene.NET。
Mostly interested in peak HTTP request figures as this is what they need to make sure they can handle.
讓人很感興趣的是他們如何處理訪問高峰時的HTTP請求。
All properties now run on the same Stack Exchange platform. That means Stack Overflow, Super User, Server Fault, Meta, WebApps, and Meta Web Apps are all running on the same software.
所有這些都運行于Stack Exchange平臺，那意味著Stack Overflow, Super User, Server Fault, Meta, WebApps, 和Meta Web Apps都運行于同一個軟件。
There are separate StackExchange sites because people have different sets of expertise that shouldn't cross over to different topic sites. You can be the greatest chef in the world, but that doesn't qualify you for fixing a server.
也有一些獨立運行的StackExchange站點，服務于那些具有多個專業技能，又不想為了不同的話題在多個站點之間奔波的人。如果你能成為最偉大的主廚，不能因為給你安排了服務員的工作，你就安于現狀。
They aggressively cache everything.
他們瘋狂地使用緩存。
All pages accessed by (and subsequently served to) annonymous users are cached via Output Caching.
未登錄用戶訪問的所有頁面都通過Output Caching進行緩存。
Each site has 3 distinct caches: local, site, global.
每個站點使用三種類型的緩存：本地、站點、全局。
local cache: can only be accessed from 1 server/site pair
本地緩存：只能被當前站點的當前服務器訪問。
- To limit network latency they use a local "L1" cache, basically HttpRuntime.Cache, of recently set/read values on a server. This would reduce the cache lookup overhead to 0 bytes on the network.
  為了減少網絡延時，通常使用HttpRuntime.Cache作為一級緩存，這樣可以避免通過網絡在緩存服務器上查找的開銷。
- Contains things like user sessions, and pending view count updates.
  緩存內容包含用戶會話，視圖數的更新。
- This resides purely in memory, no network or DB access.
  直接緩存在內存中。
site cache: can be accessed by any instance (on any server) of a single site
站點級緩存：能被同一個站點的所有服務器訪問。
- Most cached values go here, things like hot question id lists and user acceptance rates are good examples
  大部分的緩存都在這一級，比如熱點問題ID列表，用戶支持率。
- This resides in Redis (in a distinct DB, purely for easier debugging)
  緩存數據存儲在Redis數據庫中。
- Redis is so fast that the slowest part of a cache lookup is the time spent reading and writing bytes to the network.
  Redis速度很快，緩存查找的開銷主要在網絡傳輸上。
- Values are compressed before sending them to Redis. They have plenty of CPU and most of their data are strings so they get a great compression ratio.
  緩存數據發送至Redis之前會被壓縮。為什么要壓縮呢？因為CPU資源綽綽有余，而且大部分緩存數據是字符串，壓縮率會很高，何樂而不為呢。
- The CPU usage on their Redis machines is 0%.
  Redis服務器上的CPU使用率是0%。
global cache: which is shared amongst all sites and servers
全局緩存：被所有站點和服務器共享。
- Inboxes, API usage quotas, and a few other truly global things live here
  緩存內容包含收件箱，API使用限額，一些全局設置等。
- This resides in Redis (in DB 0, likewise for easier debugging)
  緩存于Redis數據庫中。
Most items in the cache expire after a timeout period (a few minutes usually) and are never explicitly removed. When a specific cache invalidation is required they use Redis messaging to publish removal notices to the "L1" caches.
大部分緩存項目在超過緩存時間之后會自動過期（通常幾分鐘），不需要進行刪除操作。當需要讓一個特定的緩存失效，會通過Redis消息系統給一級緩存發送刪除通知。
Joel Spolsky is not a Microsoft Loyalist, he doesn't make the technical decisions for Stack Overflow, and considers Microsoft licensing a rounding error. Consider yourself corrected Hacker News commentor.
Joel Spolsky（Stack Overflow的創始人）并不是微軟的忠誠分子，他不負責技術決策，使用微軟軟件考慮的也只是性價比。Hacker News上一些評論者的說法需要糾正。
For their IO system they selected a RAID 10 array of Intel X25 solid state drives . The RAID array eased any concerns about reliability and the SSD drives performed really well in comparision to FusionIO at a much cheaper price.
對于IO系統，他們選擇的是Intel X25 solid state drives(SSD硬盤)的RAID 10磁盤陣列，這樣的磁盤陣列，保證了可靠性。這個SSD硬盤用起來感覺不錯，而且價格比FusionIO的便宜。
The full boat cost for their Microsoft licenses would be approximately $242K. Since Stack Overflow is using Bizspark they are not paying near the full sticker price, but that's the max they could pay.
使用的這些微軟軟件，如果全部購買的話，總費用大概在24.2萬美元。由于Stack Overflow參加了微軟的Bizspark計劃，所以不需要付這么多錢，但是要付的話，最多也就是這么多。