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Engineering a Content Delivery Network
Bruce Maggs
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The Akamai Platform and Services
215,000+ Servers 1,300+ Networks 3,300+ Physical Locations 750+ Cities 120+ Countries A Global Platform: Delivering Content for 130,000+ Domains All top 20 global ecommerce sites All top 30 media & entertainment companies 16 of the top 20 global banks All major anti-virus software vendors Daily Statistics: 30+ Tbps traffic served 600+ million IPv4 addresses seen 3+ trillion requests served 260+ terabytes compressed logs
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Part I: Services http://www.microsoft.com (DNS)
(images) (DDoS protection)
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Design Themes Redundancy Self-assessment Fail-over at multiple levels Robust algorithms
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FirstPoint – DNS (e.g., Microsoft!)
Selects from among several mirror sites operated by content provider
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Embedded Image Delivery (e.g., Facebook)
Embedded URLs are Converted to ARLs ak <html> <head> <title>Welcome to xyz.com!</title> </head> <body> <img src=“ <h1>Welcome to our Web site!</h1> <a href=“page2.html”>Click here to enter</a> </body> </html> Very simple process.
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Akamai DNS Resolution 4 6 5 8 7 9 select cluster 3 10 11 12 13
xyz.com .com .net Root (Verisign) xyz.com’s nameserver 6 ak.xyz.com 5 akamai.net 8 7 a212.g.akamai.net 9 select cluster Local Name Server 3 Akamai High-Level DNS Servers 10 g.akamai.net 11 Akamai Low-Level DNS Servers 12 a212.g.akamai.net One of many ways—don’t have to do cname but it is easy. Note that usually address is already in local name server and you don’t do all these steps. 13 End User select servers within cluster 16 1 Browser’s Cache 14 OS 2 15
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Live Streaming Architecture
x Satellite Uplink Satellite Downlink Encoding Top-level reflectors X Entry Point X X X X x Regions
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SiteShield (www.fbi.gov)
A K M I Hacker! A K M I Hacker! Content provider’s website A K M I Hacker!
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Part II: Failures Hardware Network Software Configuration
Misperceptions Attacks
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Hardware / Server Failures
Linux boxes with large RAM and disk capacity, Windows servers Sample Failures: Memory SIMMS jumping out of their sockets Network cards screwed down but not in slot Etc.
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Akamai Cluster Servers pool resources RAM Disk Throughput
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View of Clusters buddy suspended hardware failure odd man out
datacenter
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Network Failures E.g., congestion at public and private peering points, misconfigured routers, inaccessible networks, etc., etc., etc.
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Core Points X 1 2 3 4 Core point X is the first router at which all paths to nameservers 1, 2, 3, and 4 intersect. X can be viewed as the straddling the core and the edge of the network.
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7,000 account for 95% end-user load
Core Points 500,000 nameservers reduced to 90,000 core points 7,000 account for 95% end-user load
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Engineering Methodology
C programming language (gcc). Reliance on open-source code. Large distributed testing systems. Burn-in on “invisible” system. Staged rollout to production. Backwards compatibility.
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Perceived Failures Examples Personal firewalls Reporting tools
Customer-side problems Third-party measurements
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