How does saint mode work when director is being used?

Stroomer, Jeff Jeff.Stroomer at
Tue Dec 27 19:22:46 CET 2011

Varnish folks,

How does saint mode work when a director is being used?  The discussion here

mentions this case briefly, but doesn't have much detail.

To make this more concrete, let's say I am using a round-robin director to distribute traffic across three back ends named A, B, and C, and suppose that in vcl_fetch I see a 500 response that came from A.  If I set saint mode to 20 seconds on the response, does that mean that the object is blacklisted on A for 20 seconds, and therefore subsequent requests for that object  go to B and C?   And if  saint mode subsequently also blacklists the object on B and C as well, does that mean that grace mode kicks in, and a cached copy is returned?

Assuming I have this right, then it sounds like the backend health checks used by the director are a large-scale way to blacklist all requests for a back end, whereas saint mode is a small-scale object-by-object way to blacklist a back end.

Thanks in advance for the help,

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