Mailing List Archive: [lvs-users] How ldirectord polls real servers

[lvs-users] How ldirectord polls real servers

Apr 23, 2013, 8:42 AM

Post #1 of 3 (1408 views)

Hi,
as far as you know where can I find a detailed description/documentation
about how ldirectord polls the realservers in order to realize if the node
should be actually removed from the cluster?

For sure, " ldirectord monitors the health of the real servers by
periodically requesting a known URL and checking that the response contains
an expected response. If a real server fails then the server is removed and
will be reactivated once it comes back on line.".

But what if the real servers implement a custom tcp or udp service?
In case of a tcp persistent connection, what if there is no data flow for a
while (shall I rely just on the 'persistent' timeout)?
And what about a cistom udp server?

Is there a way to use tcpdump in order to detect such evidence?

Thanks in advance for your advice,
Regards
G.

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Re: [lvs-users] How ldirectord polls real servers [ In reply to ]

malcolm at loadbalancer

Apr 23, 2013, 9:26 AM

Post #2 of 3 (1348 views)

Permalink

Gugliemo,

Ldirectord has various different health checking methods.

For a simple TCP based service you could use the 'connect' check i.e.
Can I do a TCP open on that port?
For UDP you would probably just use a ping check as it is connectionless.

The various methods are pretty well documented in the man page.

On 23 April 2013 16:42, Guglielmo Abbruzzese <g.abbruzzese@resi.it> wrote:
> Hi,
> as far as you know where can I find a detailed description/documentation
> about how ldirectord polls the realservers in order to realize if the node
> should be actually removed from the cluster?
>
> For sure, " ldirectord monitors the health of the real servers by
> periodically requesting a known URL and checking that the response contains
> an expected response. If a real server fails then the server is removed and
> will be reactivated once it comes back on line.".
>
> But what if the real servers implement a custom tcp or udp service?
> In case of a tcp persistent connection, what if there is no data flow for a
> while (shall I rely just on the 'persistent' timeout)?
> And what about a cistom udp server?
>
> Is there a way to use tcpdump in order to detect such evidence?
>
> Thanks in advance for your advice,
> Regards
> G.
>
>
>
> _______________________________________________
> Please read the documentation before posting - it's available at:
> http://www.linuxvirtualserver.org/
>
> LinuxVirtualServer.org mailing list - lvs-users@LinuxVirtualServer.org
> Send requests to lvs-users-request@LinuxVirtualServer.org
> or go to http://lists.graemef.net/mailman/listinfo/lvs-users

--
Regards,

Malcolm Turnbull.

Loadbalancer.org Ltd.
Phone: +44 (0)870 443 8779
http://www.loadbalancer.org/

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Re: [lvs-users] How ldirectord polls real servers [ In reply to ]

wferi at niif

Apr 23, 2013, 10:39 AM

Post #3 of 3 (1345 views)

Permalink

"Guglielmo Abbruzzese" <g.abbruzzese@resi.it> writes:

> But what if the real servers implement a custom tcp or udp service?

For example, here's how one could implement a custom HTTP check:

service=simpletcp
checkport=80
request="GET / HTTP 1.0\n\n"
receive="<html><body><h1>It works!</h1></body></html>"

You can easily tailor it to your custom TCP service.
I don't really understand your other questions, sorry.
--
Regards,
Feri.

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