Grace mode with 404 responses?

[Peter Loron]

Hello, folks. I’m testing a Varnish 4.1.1 setup. Specifically I’m working with shielding a client service from an unreliable remote service by proxying and caching responses from the remote system.

Grace mode is working fine for situations where the remote server is unresponsive (e.g. apache turned off), but does not seem to work when a 404 is returned for a resource. I immediately get the 404 on the client when the TTL (not the TTL + grace) is expired.

I’m assuming this is something I’m not doing right in my VCL file, but I can’t figure out what.

Is there a canonical example of how to handle this properly?

Thanks.

-Pete