[squid-users] Originserver load balancing and health checks in Squid reverse proxy mode

[Chris]

Hi,

thank you Amos, this is bringing me into the right direction.

Now I know what I'll have to debug: the pinger.

Cache.log shows:

2021/02/09 14:49:27| pinger: Initialising ICMP pinger ...
2021/02/09 14:49:27| pinger: ICMP socket opened.
2021/02/09 14:49:27| pinger: ICMPv6 socket opened
2021/02/09 14:49:27| Pinger exiting.

and that last line "pinger exiting" looks like a problem here.

Squid is used as a package from ubuntu bionic, it's configured with 
"--enable-icmp" as stated by squid -v.

Now I explicitly wrote a "pinger_enable on" and the pinger_program path 
(in this case: "/usr/lib/squid/pinger" ) into the squid.conf  (as well 
as icmp_query on) and reconfigured but the cache.log still shows:

"Pinger exiting"

So I don't understand why the pinger is exiting. The pinger_program is 
owned by root and has 0755 execution rights. Normal ping commands do 
work and show the one originserver at ttl=53 and time=50 while the other 
is at ttl=56 and time=155 - so a RTT comparison for weighted-round-robin 
should work here.

Any hints on how I can find out why the pinger is exiting? Right now I'm 
debuging with debug_options ALL,1 44,3 15,8 but don't see a reason why 
the pinger exits.

The Originservers are defined by (with icp/htcp disabled):

cache_peer [ipv4_address_srv1] parent [http_port] 0 no-digest 
no-netdb-exchange weighted-round-robin originserver name=srv1 
forceddomain=[domainname]

cache_peer [ipv4_address_srv2] parent [http_port] 0 no-digest 
no-netdb-exchange weighted-round-robin originserver name=srv2 
forceddomain=[domainname]


Thank you for your help,

Chris





On 09.02.21 04:23, Amos Jeffries wrote:
> 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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