Determine if grace object is available

[Dridi Boukelmoune]

Hi Mattias,

Have you tried something with a restart ? You could decide for
instance to change the backend to maintenance and restart if
you're in vcl_error and backend is not healthy.

Cheers,
Dridi

On Wed, Jul 30, 2014 at 9:38 AM, Mattias Geniar <mattias at nucleus.be> wrote:
>
>>> 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 backend
> here?
>   set req.backend = maintenance_backend;  # This could serve static pages
> with maintenance info
> }
>
>
> I'm thing 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;
> }
>
> Thanks,
>
> Mattias
>
>
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