Determine if grace object is available

Mattias Geniar mattias at
Fri Oct 24 09:41:45 CEST 2014

>I¹d like to get fancy with grace stored objects, but I¹m not sure how
>>>to do this. Can I determine if there¹s a grace object I could deliver?
>>>Basically I want my logic to be:
>As a follow-up to this thread, I'm wondering if the following is possible,
>given that there is a director present with 2 servers, having health
>probes configured.
>If the director has no healthy backends;
>1. See if a grace object is available, if so, deliver it
>2. If no grace object is available, change the backend to a "maintenance"
>one to serve a static HTML page for maintenance purposes
>The struggle is in vcl_recv {}, how would this be able to work? If I use
>req.backend.healthy to determine the backend health to set a new backend,
>I lose the grace ability (as it'll be passed to the new, available,
>backend?). Or I'm missing something here.
># Use grace, when available and when needed
>if (! req.backend.healthy) {
>  # Backends are sick, so fall back to a stale object, if possible
>  set req.grace = 5m;
>  # If no stale object is available, how should we switch to a new
>  set req.backend = maintenance_backend;  # This could serve static pages
>with maintenance info
>I'm thinking something like this, but it's not possible?
>if (req.grace.available) {
>  set req.grace = 5m;
>} else {
>  # No grace object available, set new backend
>  set req.backend = maintenance_backend;

Did anyone have any valuable input on this, or should we just assume it's
not possible in the current versions?



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