Arista Networks: Caching the BODY of a POST request for subsequent GETs

[Reza Naghibi]

I think what you are looking for is write through caching behavior? This is
not possible with open source. However, it's fully supported in the
enterprise version.


---
Reza Naghibi
VP of Technology
Varnish Software


On Sun, May 17, 2020 at 10:48 AM Guillaume Quintard <
guillaume at varnish-software.com> wrote:

> Hi Sidharta,
>
> I'm not sure why the tutorial you linked to isn't adequate. Do you need
> the POST to also create an object in cache?
>
> Kind regards,
>
> --
> Guillaume Quintard
>
>
> On Sat, May 16, 2020 at 11:44 PM Sidhartha Agrawal <sid at arista.com> wrote:
>
>> Hi Varnish Community,
>>
>> I am a software developer at Arista Network in our Tools and
>> Infrastructure Group. We use Varnish(6.3.1) to cache our build objects such
>> as RPMS and images and Varnish is an integral part of our internal build
>> system.
>>
>> Some of these objects are of the order of ~500 MB, so a GET of multiple
>> such objects can put a significant load on the backend(OpenSwift). Since
>> there is an adequate temporal locality(within a day) between the POST of
>> the large object and the subsequent GET, we would like to cache the object
>> when the POST happens, so that the subsequent GET is guaranteed to find it
>> in the cache(unless evicted or expired).
>>
>> As I understand, Varnish bypasses the cache for POST and passes it
>> straight to the backend. We would like to change this behavior of POST to
>> also add an entry for the object in the cache if the write to the backend
>> was successful.
>>
>> A cursory google search for “Caching Post requests on Varnish” lead to
>> me this article
>> <https://docs.varnish-software.com/tutorials/caching-post-requests/#step-1-prepare-the-vcl-for-caching-post-requests>.
>> Though I do not think this is exactly what we need. The article talks about
>> avoiding a write to the backend if another POST request is made with the
>> same body. That is different from what we are trying to do.
>>
>> I would appreciate any insights you can provide in to:
>>
>>    -
>>
>>    What changes do I need to make to the VCL to achieve our desired
>>    behavior
>>    -
>>
>>    Comments, on whether this is a bad idea for some reason.
>>
>>
>> I have been following the VCL state machine from this website
>> <https://varnish-cache.org/docs/6.3/reference/states.html#reference-states>.
>> I appreciate the help.
>>
>> -Sid
>>
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