Optimal route selection in a content delivery network
A routing mechanism, service or system operable in a distributed networking environment. One preferred environment is a content delivery network (CDN) wherein the present invention provides improved connectivity back to an origin server, especially for HTTP traffic. In a CDN, edge servers are typically organized into regions, with each region comprising a set of content servers that preferably operate in a peer-to-peer manner and share data across a common backbone such as a local area network (LAN). The inventive routing technique enables an edge server operating within a given CDN region to retrieve content (cacheable, non-cacheable and the like) from an origin server more efficiently by selectively routing through the CDN's own nodes, thereby avoiding network congestion and hot spots. The invention enables an edge server to fetch content from an origin server through an intermediate CDN server or, more generally, enables an edge server within a given first region to fetch content from the origin server through an intermediate CDN region.
1. A method operative in a content delivery network having a set of server nodes organized into regions, wherein the server nodes provide delivery of content on behalf of participating content providers, comprising:
for a given content provider origin server, generating a map identifying a set of alternate paths that may be used for edge server to content provider origin server communications, wherein the map identifies a set of alternate paths, and wherein each alternate path includes at least one content delivery network server node;
upon receipt at a particular edge server of a request for an object, determining whether the object is available for delivery from the particular edge server;
if the object is not available for delivery from the particular edge server, selecting a path over which the particular edge server should go forward to the content provider origin server to attempt to obtain the object, wherein the path is selected from one of the alternate paths identified in the map; and
issuing a new request for the object from the particular edge server over the path.
2. The method as described in claim 1 wherein the new request is issued to the content delivery network server node on the path.
3. The method as described in claim 1 wherein the object is content that is generated at the content provider origin server or is non-cacheable at the particular edge server.
4. The method as described in claim 1 wherein the path over which the particular edge server should go forward to the content provider origin server is valid for a given time period.
5. The method as described in claim 1 further including periodically updating the map to reflect changing Internet conditions.
6. The method as described in claim 1 wherein the path is determined by the particular edge server as a result of performing a performance test.
7. The method as described in claim 6 wherein the performance test comprises a race, wherein the race comprises downloading a file to the particular edge server over at least the alternate paths.
8. The method as described in claim 7 wherein the race is executed by the particular edge server upon receipt of the request for the object.
9. The method as described in claim 8 wherein the file that is downloaded during the race is also the object.
10. A method operative in a content delivery network having a set of content servers organized into regions, wherein the content servers provide delivery of content on behalf of participating content providers, and wherein a given content provider origin server may be reached over a set of paths including a default BGP path and a set of alternate paths, wherein at least one path of the set of alternate paths includes an intermediate content delivery network content server, comprising:
for each of a set of participating content providers, provisioning the content servers in the content delivery network to enable the content servers to fetch content from the participating content provider's origin server over an alternate path of the set of alternate paths instead of using the default BGP path;
upon receipt at a content server of a request for an object, determining whether the object is available for delivery from the content server;
if the object is not available for delivery from the content server, issuing a new request for the object from the content server, wherein the new request is issued over one of the alternate paths;
receiving the object at the content server over the alternate path; and
serving the object from the content server.