From this thread in the forums: http://forum.nginx.org/read.php?2,214606,215664#msg-215664
Seems like NGINX does not do the setup I described very well and delivers stale cached files - I quote:
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> That's not currently doable with nginx. Proxy_cache_use_stale directive works when you've got your backend down.
> What you want is more like doing a triggered update of the content in background and it's not possible at this time.
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But confusingly, another post on thread states:
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>proxy_cache_use_stale updating does soemthing similar.
>You may could do something like (from the docs)
>proxy_cache_bypass $http_my_secret_header;
>without a corresponding proxy_no_cache and that should make nginx go to the origin server but cache the results.
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As mentioned in the referenced thread, I am already looking at Varnish also.