How to cache req.body and then use it in response for coming requests in varnish

[Guillaume Quintard]

Hi,

then you need something like
https://docs.varnish-software.com/varnish-cache-plus/vmods/synthbackend/ (with
the .mirror() function) which was created for this purpose, but it's a
Varnish Plus feature.

It may be possible usable with the new backend error mechanism in the next
version, coupled with some vmod_bodyaccess feature (but you would need a
blob instead of a string)

-- 
Guillaume Quintard


On Mon, Aug 12, 2019 at 12:57 AM Yuan Zafir <eyz12315 at live.cn> wrote:

> hi Guillaume，
>
> Thanks for your reply.
>
> I think there should be ambiguity description about my question in my
> first mail.
> Actually what I want is to use varnish as a cache service *without backend
> servers*,  clients can push/pull the resource to/from varnish cache storage
> using specific http method, such as POST/GET.
> For example, one client can send " POST /string1 "abcd" " to make a
> string-"abcd" cached into varnish, other clients could then use "GET
> /string1" request to get this string. If Get request miss the cache, a 404
> error could be sent (through synth command in vcl_miss).
>
> I am not sure whether it's feasible to make the string-"abcd" cached into
> varnish. Do you have any recommendation for this requrement?
> Thanks again for your attention!
>
>
> Zafir Yuan
>
> ------------------------------
> eyz12315 at live.cn
>
>
> *From:* Guillaume Quintard <guillaume at varnish-software.com>
> *Date:* 2019-08-12 14:03
> *To:* Yuan Zafir <eyz12315 at live.cn>
> *CC:* varnish-misc <varnish-misc at varnish-cache.org>
> *Subject:* Re: How to cache req.body and then use it in response for
> coming requests in varnish
> Hi,
>
> There are a few things to do here:
> - make sure that if req.method == "POST", you return(hash) from vcl_recv
> (otherwise, the builtin.vcl (
> https://github.com/varnish/Varnish-Cache/blob/4.1/bin/varnishd/builtin.vcl#L63)
> will pass)
> - but before that, add 'set req.http.x-method = req.method' at the top of
> vcl_recv, and 'if (bereq.http.x-method == "POST") {set bereq.method =
> "POST"; }' at the top of vcl_backend_fetch, because for cacheable request,
> varnish will want to set the method to "GET", so we need to reset it back
>
> On top of that:
> - you can use req.hash_always_miss (man vcl) to push new content (and
> avoid just getting the cached response)
> - make sure you only cache when the response is OK, otherwise a wrong POST
> request will mask the previous valid ones
> - if you are acting upon the URL of the resource itself, I'd say it should
> be a PUT/PATCH, rather than a POST, but that's just pedantry at this point
> - realize that the content cached is the response returned by the backend,
> not the body of the request itself. They may be the same, but maybe not
> (there are ways to do it though)
>
> Hope that helps
> --
> Guillaume Quintard
>
>
> On Sun, Aug 11, 2019 at 10:42 PM Yuan Zafir <eyz12315 at live.cn> wrote:
>
>> Hi，I am trying to configure varnish as a simple cache service, which
>> means the content posted by clients could be cached as an object. The
>> content chould be returned in responses for the coming GET requests(with
>> same url...). I am not sure wether this can be realized by VCL
>> configuration.
>>
>> Any recommendation for this situation? Thanks for any help!
>>
>> I was noticed vmod-bodyaccess can cache req.body and then it could be
>> used in bereq(
>> https://info.varnish-software.com/blog/caching-post-requests-with-varnish),
>> but I do not know how to put it into responses for clients.
>>
>> thanks!
>> Zafir
>> ------------------------------
>> eyz12315 at live.cn
>> _______________________________________________
>> varnish-misc mailing list
>> varnish-misc at varnish-cache.org
>> https://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc
>>
>
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