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Bài giảng Mạng máy tính nâng cao: Content distribution networks cung cấp cho người học các kiến thức: Single server, poor performance, web caching, limitations of web caching, content distribution networks,... Mời các bạn cùng tham khảo.
Content Distribution Networks (CDNs) MẠNG MÁY TÍNH NÂNG CAO CuuDuongThanCong.com https://fb.com/tailieudientucntt Single Server, Poor Performance qSingle server § Single point of failure § Easily overloaded § Far from most clients qPopular content § Popular site § “Flash crowd” (aka “Slashdot effect”) § Denial of Service attack CuuDuongThanCong.com https://fb.com/tailieudientucntt Web Caching CuuDuongThanCong.com https://fb.com/tailieudientucntt Proxy Caches origin server qReactively replicates Proxy popular content server qSmaller round-trip client times to clients qReduces load on origin servers client qReduces network load, and bandwidth costs qMaintain persistent TCP connections CuuDuongThanCong.com https://fb.com/tailieudientucntt Forward Proxy qCache close to the client § Improves client performance client § Reduces network provider’s costs Proxy server qExplicit proxy § Requires configuring browser qImplicit proxy client § Service provider deploys an “on path” proxy § … that intercepts and handles Web requests CuuDuongThanCong.com https://fb.com/tailieudientucntt Reverse Proxy qCache close to server origin server § Improve client performance § Reduce content provider cost § Load balancing, content assembly, transcoding, etc Proxy server qDirecting clients to the proxy § Map the site name to the IP address of the proxy CuuDuongThanCong.com origin server https://fb.com/tailieudientucntt Google Design Servers Data Centers Servers Router Router Private Backbone Reverse Proxy Reverse Proxy Internet Requests CuuDuongThanCong.com Client Client Client https://fb.com/tailieudientucntt Limitations of Web Caching qMuch content is not cacheable § Dynamic data: stock prices, scores, web cams § CGI scripts: results depend on parameters § Cookies: results may depend on passed data § SSL: encrypted data is not cacheable § Analytics: owner wants to measure hits qStale data § Or, overhead of refreshing the cached data CuuDuongThanCong.com https://fb.com/tailieudientucntt Content Distribution Networks CuuDuongThanCong.com https://fb.com/tailieudientucntt Content Distribution Network origin server in North America qProactive content replication § Content provider (e.g., CNN) contracts with a CDN qCDN replicates the content CDN distribution node § On many servers spread throughout the Internet qUpdating the replicas § Updates pushed to replicas when CDN server the content changes CDN server in S America CDN server in Asia in Europe CuuDuongThanCong.com https://fb.com/tailieudientucntt 10 Server Selection Policy qLive server § For availability Requires continuous monitoring of liveness, load, and performance qLowest load § To balance load across the servers qClosest § Nearest geographically, or in round-trip time qBest performance § Throughput, latency, … qCheapest bandwidth, electricity, … CuuDuongThanCong.com https://fb.com/tailieudientucntt 11 12 Server Selection Mechanism qApplication § HTTP redirection § Fine-grain control § Selection based on client IP address qDisadvantages GET Redirect GET OK CuuDuongThanCong.com qAdvantages § Extra round-trips for TCP connection to server § Overhead on the server https://fb.com/tailieudientucntt 13 Server Selection Mechanism qRouting § Anycast routing qAdvantages § No extra round trips § Route to nearby server qDisadvantages 1.2.3.0/24 § Does not consider network or server load § Different packets may go to different servers § Used only for simple request-response apps 1.2.3.0/24 CuuDuongThanCong.com https://fb.com/tailieudientucntt Server Selection Mechanism qNaming qAdvantages § DNS-based server selection 1.2.3.4 § Avoid TCP set-up delay § DNS caching reduces overhead § Relatively fine control qDisadvantage DNS query 1.2.3.5 local DNS server CuuDuongThanCong.com § Based on IP address of local DNS server § “Hidden load” effect § DNS TTL limits adaptation 14 https://fb.com/tailieudientucntt How Akamai Works 15 CuuDuongThanCong.com https://fb.com/tailieudientucntt Akamai Statistics qDistributed servers § Servers: ~61,000 § Networks: ~1,000 § Countries: ~70 qMany customers § Apple, BBC, FOX, GM IBM, MTV, NASA, NBC, NFL, NPR, Puma, Red Bull, Rutgers, SAP, … qClient requests § Hundreds of billions per day § Half in the top 45 networks § 15-20% of all Web traffic worldwide 16 CuuDuongThanCong.com https://fb.com/tailieudientucntt 17 How Akamai Uses DNS cnn.com (content provider) DNS root server GET index html HTTP http://cache.cnn.com/foo.jpg HTTP Akamai global DNS server Akamai cluster Akamai regional DNS server Nearby Akamai cluster End user CuuDuongThanCong.com https://fb.com/tailieudientucntt 18 How Akamai Uses DNS cnn.com (content provider) DNS root server DNS lookup cache.cnn.com HTTP Akamai global DNS server ALIAS: g.akamai.net Akamai regional DNS server Nearby Akamai cluster End user CuuDuongThanCong.com Akamai cluster https://fb.com/tailieudientucntt 19 How Akamai Uses DNS cnn.com (content provider) DNS root server DNS lookup g.akamai.net HTTP ALIAS a73.g.akamai.net Akamai global DNS server Akamai regional DNS server Nearby Akamai cluster End user CuuDuongThanCong.com Akamai cluster https://fb.com/tailieudientucntt 20 How Akamai Uses DNS cnn.com (content provider) HTTP DNS root server Akamai global DNS server Akamai cluster Akamai regional DNS server Address 1.2.3.4 Nearby Akamai cluster End user CuuDuongThanCong.com https://fb.com/tailieudientucntt 21 How Akamai Uses DNS cnn.com (content provider) DNS root server HTTP Akamai global DNS server Akamai cluster Akamai regional DNS server End user Nearby Akamai cluster GET /foo.jpg Host: cache.cnn.com CuuDuongThanCong.com https://fb.com/tailieudientucntt 22 How Akamai Uses DNS cnn.com (content provider) DNS root server GET foo.jpg 11 12 HTTP Akamai global DNS server Akamai cluster Akamai regional DNS server End user Nearby Akamai cluster GET /foo.jpg Host: cache.cnn.com CuuDuongThanCong.com https://fb.com/tailieudientucntt 23 How Akamai Uses DNS cnn.com (content provider) DNS root server 11 12 HTTP Akamai global DNS server Akamai cluster Akamai regional DNS server End user CuuDuongThanCong.com Nearby Akamai cluster 10 https://fb.com/tailieudientucntt How Akamai Works: Cache Hit cnn.com (content provider) GET index html DNS root server Akamai server Akamai high-level DNS server Akamai low-level DNS server Nearby hash-chosen Akamai server End user 10 GET /cnn.com/foo.jpg CuuDuongThanCong.com https://fb.com/tailieudientucntt 24 Hỏi & Đáp Khoa Công nghệ thông tin - Đại học Khoa học tự nhiên TPhttps://fb.com/tailieudientucntt Hồ Chí Minh CuuDuongThanCong.com 25 ... https://fb.com/tailieudientucntt Content Distribution Networks CuuDuongThanCong.com https://fb.com/tailieudientucntt Content Distribution Network origin server in North America qProactive content replication § Content. .. Akamai Works: Cache Hit cnn.com (content provider) GET index html DNS root server Akamai server Akamai high-level DNS server Akamai low-level DNS server Nearby hash-chosen Akamai server End user... request-response apps 1.2.3.0/24 CuuDuongThanCong.com https://fb.com/tailieudientucntt Server Selection Mechanism qNaming qAdvantages § DNS-based server selection 1.2.3.4 § Avoid TCP set-up delay