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HTTP vs. DNS for request redirection in CDNs

Redirect (Photo credit: Wikipedia)
The two most common ways to redirect requests in content delivery networks (CDNs) rely on the features of the domain name system (DNS) and on the redirection message of the Hypertext transfer protocol (HTTP). This article explains the strengths and weaknesses of both methods.

HTTP redirection is heavy but powerful 

  • HTTP is a heavy protocol: aueries not easy to parse for machines (human readable) 
  • HTTP requires one redirection by request (few browsers cache HTTP 302 and HTTP 307 messages)
  • The request redirector sees the full details of the requests: full URL, IP address of the end user, etc.

DNS is more scalable but less flexible than HTTP

  • Caching of DNS records complexifies load balancing
  • But… makes DNS redirection scalable: there is only 1 redirection when several objects are from the same fully qualified domain name (FQDN)
  • The request router picks a cache based on the DNS request: 
    • It sees only the DNS server's IP address (except if some DNS extensions are used) and thereby geolocates the end-user inaccurately
    • It does not see the full URL: just the FQDN


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