Server side cache selection
Some CDNs provide access to a server-side cache selection (SSCS) interface. This allows an application such as CDN selector to ask for the details of the best cache to serve a particular request, and send its URL to the client.
Without this step, the client would have to interact with the request router itself, which typically involves a DNS request or HTTP redirection.
The advantages of using server-side cache selection are:
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Quicker access to content in many cases
The client doesn't have to make a separate HTTP and/or DNS request to the CDN for routing. -
The CDN selector gets visibility of the health of the CDN
The response from the routing service will indicate whether a particular request can be handled or not. If the routing request fails due to heavy load, or is denied due to misconfiguration, then CDN selector can react by failing over to an alternative CDN.
The CDN selector can also assume that if the interface is non-responsive then the CDN is in bad health, and an alternative should be used.
Currently CDN selector supports this feature for the following CDNs:
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Velocix (SSCSv2 interface)
you must activate this feature in the Velocix Admin Console and add the IP address(es) of CDN selector frontends.
When creating or editing a CDN, the CDN Type field will be used to determine whether Server-Side Request Routing can be used.
If it is supported for the current CDN Type, then a field will appear allowing you to type in the URL of the Server Side Cache Selection interface.
When you go to use this CDN in a distribution there is no need to configure a hostname, since this will by dynamically set using the SSCS request.
Server Side cache selection happens towards the end of the request flow, after the top choice CDN has been identified.
If the top choice CDN has this feature enabled, a request will be sent to the CDN request router which will indicate whether the CDN is capable of serving the request, and which cache should be used.
