Re: Informal meeting on blind caching

On 27/07/2016 11:33, Richard Bradbury wrote:
> On 17/07/2016 18:03, Martin Thomson wrote:
>> We are having a meeting on blind caching on Tuesday 08:30 in
>> Charlottenburg I.  Folks who are interested are invited to join us.
>>
>> Rough agenda is to discuss what this is, the status of specs and
>> implementations.  Then we are looking to get some input on the work
>> that has been done and what might need to happen next.
>>
>> For those not familiar with this, the following drafts are recommended reading:
>> https://tools.ietf.org/html/draft-thomson-http-scd
>> https://tools.ietf.org/html/draft-thomson-http-bc
>> https://tools.ietf.org/html/draft-reschke-http-oob-encoding
>> https://tools.ietf.org/html/draft-thomson-http-mice
>> https://tools.ietf.org/html/draft-ietf-httpbis-encryption-encoding
>
> Hi. Thanks for an interesting session last week.
>
> Based on my reading of the Internet Drafts I think these are the two 
> main Use Cases under consideration here:
>
>  1. *Blind caching in a CDN edge cache that is acting as a delegated
>     origin server.*
>       * Described in draft-thomson-http-scd.
>       * Making use of the techniques described in
>         draft-reschke-http-oob-encoding, draft-thomson-http-mice and
>         draft-ietf-httpbis-encryption-encoding.
>  2. *Blind caching in an explicitly configured proxy server.*
>       * Described in draft-thomson-http-bc.
>       * Making use of the techniques described in
>         draft-reschke-http-oob-encoding, draft-thomson-http-mice and
>         draft-ietf-httpbis-encryption-encoding.
>
> The discussion in Berlin last Tuesday morning flowed fairly freely 
> between the two Use Cases, so I just wanted to check my understanding.
>

OK. Now I feed I understand Use Case 2 better, I attach a couple of 
sequences describing my (incomplete) understanding of Use Case 1 above. 
The main question in my mind here is whether the resources are 
explicitly pushed into the CDN cache (what I have called "Mode P") or 
whether they are retrieved on demand from the origin server by the CDN 
only on cache miss ("Mode G").

Perhaps you are looking to support both modes of operation? The Internet 
Draft could usefully clarify this.

*Mode G*
    In the cache pull-through mode, there appears to be a requirement
    for the CDN to know the resource mapping in order to support the URL
    obfuscation feature. But that appears to negate one of the key
    benefits of the feature – keeping the mapping secret from the CDN
    provider. I'm clearly missing something here. Or maybe URL
    obfuscation just doesn't fly in this mode, which would be a shame
    since this is our primary mode of operation for some media types.
*Mode P*
    With the push mode, the resource mapping can remain secret to the
    origin server, which is great. But the mechanism for pushing content
    onto the CDN remains a bit of a mystery, so I have made an educated
    guess on my diagram. Perhaps you intend this mechanism to remain
    private? In which case, perhaps the Internet Draft could include a
    note to this effect?

Clarifications and comments gratefully received.


Regards,

-- 
Richard Bradbury | Lead Research Engineer
BBC Research & Development
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