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 <[email protected]> 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 > > ------------------------------ > [email protected] > > > *From:* Guillaume Quintard <[email protected]> > *Date:* 2019-08-12 14:03 > *To:* Yuan Zafir <[email protected]> > *CC:* varnish-misc <[email protected]> > *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 <[email protected]> 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 >> ------------------------------ >> [email protected] >> _______________________________________________ >> varnish-misc mailing list >> [email protected] >> https://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc >> >
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