On 10/9/19 1:34 PM, Antonio SJ Musumeci wrote: > I've a setup with N origin servers and N squid instances setup with the > intent that each squid instance is logically associated with one of the > origin servers and lists the other N-1 origin servers as other parents. > Each origin has the same immutable data but spread across buildings. I > only want them to reach out across buildings if the initial forward > fails (or perhaps is overloaded). Initial tests seem to work but they > always try the first origin server and when it fails (in this case with > a 502 as the backend of a webservice is down) it tries the second. Sounds good. > It doesn't appear that there is a negative cache on the failure. The peer up/down state is "cached", but 1) Squid does not treat an HTTP 502 response as a peer failure (even though the request may be re-forwarded after a 502 response). Roughly speaking, only TCP- and TLS-level failures are considered to be peer failures. HTTP responses, regardless of their status code, do not increment the peer failure counter AFAICT. 2) By default, a peer is not considered down after the first 9 peer failures. See cache_peer connect-fail-limit. There is also a (complicated) peer revival mechanism that may mark a previously "down" peer as "up" even though there were no HTTP requests sent to that peer IIRC. The details are complex and depend on the Squid version. > it doesn't cache the re-forward response (a 200). Is that expected? I do not think it should be expected. The number of past/failed forwarding attempts should not affect response cachability IMO. > is it possible from the logs to see the name or hostname:port of the > cache_peer being forwarded to? The following logformat %codes may be helpful here (%<a is logged by default and is given here for completeness sake): %<a Server IP address of the last server or peer connection %<A Server FQDN or peer name %<p Server port number of the last server or peer connection To log the last cache_peer_access match, you will need to use annotate_transaction ACL and %note logformat code (where available). However, IIRC, official Squids may evaluate the same matching cache_peer_access rule many times per transaction, which may result in confusing annotations. HTH, Alex. _______________________________________________ squid-users mailing list squid-users@xxxxxxxxxxxxxxxxxxxxx http://lists.squid-cache.org/listinfo/squid-users
