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

[Guillaume Quintard]

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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