How does saint mode work when director is being used?
kristian at varnish-software.com
Thu Dec 29 11:01:26 CET 2011
On Tue, Dec 27, 2011 at 10:22:46AM -0800, Stroomer, Jeff wrote:
> 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.
That's precisely it. I couldn't have said it better myself.
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