Put another way -- can I store/cache all content from the proxied upstream (up to the limits defined in proxy_cache_path), but serve from the cache only when the proxied upstream fails (e.g. timeout, error)?

We have content that should be dynamic, and hence every request should be transparently proxied. However, I want to protect against the situation when the upstream is down or having trouble. Serving a stale response (though normally undesirable), is better than returning an error.

Thank you