On 9/02/21 3:40 am, Chris wrote:
Hi all,
I'm trying to figure out the best way to use squid (version 3.5.27) in
reverse proxy mode in regard to originserver health checks and load
balancing.
So far I had been using the round-robin originserver cache peer
selection algorithm while using weight to favor originservers with
closer proximity/lower latency.
Ok.
The problem: if one cache_peer is dead it takes ages for squid to choose
the second originserver. It does look as if (e.g. if one originserver
has a weight of 32, the other of 2) squid tries the dead server several
times before accessing the other one.
The DEAD check by default requires 10 failures in a row to trigger. This
is configurable with the connect-fail-limit=N option.
Now instead of using round-robin plus weight it would be best to use
weighted-round-robin. But as I understand it, this wouldn't work with
originserver if (as it's normally the case) the originserver won't
handle icp or htcp requests. Did I miss sth. here? Would background-ping
work?
Well, kind of.
ICP/HTCP is just a protocol. Most origin servers do not support them,
but some do. Especially if the server is not a true origin but a
reverse-proxy.
I tried weighted-round-robin and background-ping on originservers but
got only an evenly distributed request handling even if ones
originservers rtt would be less than half of the others. But then again,
those originservers won't handle icp requests.
RTT is retrieved from ICMP data primarily. Check your Squid is built
with --enable-icmp, the pinger helper is operational, and that ICMP Echo
traffic is working on all possible network routes between your Squid and
the peer server(s).
So what's the best solution to a) choose the originserver with the
lowest rtt and b) still have a fast switch if one of the originservers
switches into dead state?
Check whether the RTT is actually being measured properly by Squid
(debug_options ALL,1 44,3 15,8). If the peers are fast enough responding
or close enough in the network RTT could come out as a 0 value or some N
value equal for both peer. ie. neither being "closer".
Amos
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