Using req/obj.grace to serve stale objects when backend fails

[Jeff Anderson]

> Sorry for the second post.

> I've experimented with req/obj.grace set to a few hours so a site  
> can be served even if the backend fails.  For example, with the  
> backend down and when req/obj.grace is set to several hours I can  
> open a new browser and get a 503 if I try to open a known cached  
> (and graced) page.  However if I refresh the same browser several  
> times very rapidly I finally receive the graced page.  It seems to  
> be working as expected from what I read in the documentation  
> regarding the graced object being served while the same object is  
> being fetched by another thread.  The rapid refreshing is generating  
> a second thread request which then satisifies the requirements to  
> have the graced object served.  Is there a way to configure varnish  
> to serve the cached graced object if the backend fails without the  
> browser ever seeing the 503?  Can this also be tied into the backend  
> probing/polling to serve the graced page if all the backends fail?
>
> Thanks,
> --J