Hi,
I have started writing up a suggestion following an irc discussion about
Federicos patch. I wanted to suggest to also add stale-if-error (s-i-e) support
but really I don't see a way at the moment to achieve this without added
functionality in vcl - am I missing something?
For s-i-e, I think we need to handle the case of a synchronous backend fetch (ie
one with one or more frontend requests waiting for the result) resulting in "an
error". We'd have to restart the frontend request once and check for a stale
object as in
vcl_hit {
// got here not because of grace but because of
// keep or some other parameter
if (req.restarts == 1) {
return (deliver);
}
}
The options I see at the moment to achieve this would all require additions to
VCL:
- something along the lines of a beresp.fetched ("this object originated
from a fetch initiated by this req"):
vcl_deliver {
if (beresp.fetched && req.restarts == 0 && beresp.status >= 500) {
return (restart);
}
}
OR
- some way to determine in v_b_e and v_b_r if the bereq is synchronous
and restart the req.
sub vcl_backend_(response|error) {
if (bereq.synchronous.req && beresp.status > 500) {
restart(bereq.synchronous.req);
}
}
Thanks, Nils
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