Hi,

We sometimes have a problem with the backend using its internal cache for a few 
seconds too long after something has been updated. We trigger a softpurge (xkey 
vmod) in varnish, but if someone requests the page again very soon after that, 
the data that Varnish gets from the backend might be old. In this case, we 
would like to be able to tell the backend, maybe using an extra header, that it 
should skip its internal caches and give us the updated content.

But, I'm not sure how to archive this in Varnish. Is it possible to detect that 
the page requested has been softpurged earlier? If yes, is it also possible to 
see when that softpurge took place? Because we would only ever need to do this 
if the softpurge happened less than let's say 30 seconds ago.

And the reason that the backend data might be old after an update is that what 
we call "the backend" (from a Varnish perspective) is actually a complex setup 
of services. And there, the update happens in one place, and our "backend" is 
actually a frontend server that sometimes don't get the information about the 
update quick enough. I think that the implementation of this system is a bit 
faulty, but it is what it is, and I would like to use the power of Varnish to 
handle this, if possible.
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