Hi Tamara,
On 16/06/2025 14:52, Boehm, Tamara wrote:
Thank you very much for your response.
It's interesting to learn that round-robin is considered a
non-deterministic algorithm. We assumed it was deterministic because
of its definition that requests are sent to the next backend/server
one after the other.During our experiments with HAProxy 2.8.14, we
could observe that this option has an impact on the load balancing.
Is it possible to improve theHAProxy documentation by clarifying which
algorithms are deterministic and which are not?
Ok, thanks this will be added and backported to the docs.
We have afurther question regarding the
http-keep-alive(https://www.haproxy.com/documentation/haproxy-configuration-manual/2-8r1/#4.2-option%20http-keep-alive)
property. The documentation states it's enabled by default. If the
client sends a request with the "Connection: Close" header, will
HAProxy close the connection to the backend or keep it idle?
From what I see with the oneliner below and a simple backend (nginx
serves static file), two connections to the backend (haproxy -> server
and server -> haproxy) stay idle for some short time, i.e. ~15s after
the last request with "Connection:close" header was served.
option http-keep-alive or no-option http-keep-alive does not change the
behaviour and the same if we do not have "Connection: close" in the last
request.
curl -v http://[2001:db8::1234]:8000/syslog.2.gz --output x --next
http://[2001:db8::1234]:8000/syslog.2.gz --output x --next -H
"Connection: close" http://[2001:db8::1234]:8000/syslog.2.gz --output x
backend be_transparent
mode http
option http-keep-alive
server myser 198.18.0.212:80
BR,
Best regards,
Tamara
*From: *Valentine Krasnobaeva <vkrasnoba...@haproxy.com>
*Date: *Tuesday, 10. June 2025 at 14:32
*To: *haproxy@formilux.org <haproxy@formilux.org>, Boehm, Tamara
<tamara.bo...@sap.com>
*Subject: *Re: prefer-last-server with round robin lb algo
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Hi Tamara!
Thanks for reporting this.
Non, round-robin is not deterministic, thus compatible with
prefer-last-server and this option should not be ignored.
With which version are you observing this behaviour?
"prefer-last-server" is mainly used for keepalive with servers as the
doc states and I see, that you are also using "option srvtcpka".
If you do tests with some external clients in parallel, make sure that
these clients do not close its connections with haproxy between
sending requests.
Could you provide your configuration, if possible + could you describe
in which conditions you are observing this ?
As for doc, this info about load balancing alogorithms will be added
explicitly.
In general, all supported algorithms, where hashing is envolved are
deterministic.
Kind regards,
On 03/06/2025 14:39, Boehm, Tamara wrote:
Dear community,
We are using round-robin in HAProxy as a load-balancing algorithm.
In our backend config, we use prefer-last-server as an option. But
according to the documentation
(https://www.haproxy.com/documentation/haproxy-configuration-manual/latest/#4.2-option%20prefer-last-server),
the option is only applied when the load balancing algorithm in
use is not deterministic. We could not find any examples in the
documentation of what load balancing algorithms HAProxy considers
as deterministic. According to our understanding, the round robin
algorithm is a deterministic one. Can you confirm whether our
understanding is correct that this option prefer-last-server is
fully ignored in our case?
Our config looks like:
backend http-routers-http1
mode http
balance roundrobin
option srvtcpka
no option http-server-close
option prefer-last-server
Thanks a lot and best regards,
Tamara
--
Bien cordialement,
Valentine
--
Bien cordialement,
Valentine
