Re: [lvs-users] Understanding persistence_granularity for long TCP conne

To: lvs-users@xxxxxxxxxxxxxxxxxxxxxx
Subject: Re: [lvs-users] Understanding persistence_granularity for long TCP connections and unexpected spread of traffic at reals
From: Abhijeet Rastogi <abhijeet.1989@xxxxxxxxx>
Date: Thu, 15 Aug 2019 13:19:41 -0700
Hi lvs-users,

Extremely sorry for the multiple emails, this email was stuck in the mail
queue probably because of moderation (just joined the ML) and I expected it
to get dropped so sent a different one.

Please ignore this email and look at another one, that has more clarity
with ipvsadm outputs*: *

On Wed, Aug 14, 2019 at 10:50 AM Abhijeet Rastogi <abhijeet.1989@xxxxxxxxx>

> Hi everyone,
> I'm investigating a typical configuration for an L4 TCP load balancer
> using ipvs+keepalived. Settings:-
>    - persistence_timeout: 120 seconds.  (# LVS persistence timeout, sec)
>    - /sbin/ipvsadm --set 1800 120 300
>    - persistence_granularity: "48" for ipv6.
>    - lb_algo: rr (round robin)
> My expectation is, all the IPs from the same /48 v6 subnet should always
> reach the same real_server because of setting granularity.
> However, I can see that established connections from the same /48 v6
> subnet are spread across multiple reals. (with timeouts b/w 0 seconds to
> less than 30 minutes which is a side-affect of setting higher timeout for
> TCP).
> Questions:-
>    - After the persistent_timeout expires, do new connections from the
>    same /48 subnet get assigned to a new reals based on round-robin regardless
>    of whether we've existing connections already going to a specific real from
>    that subnet? (And this results in same /48 being distributed to multiple
>    reals eventually)
>    - Is TCP timeout the reason for the unexpected spread of same /48
>    clients to multiple reals (as opposed to the expectation of 1)?
>    - If my previous question's answer is yes, should we always set
>    persistence_timeout to be higher than the TCP timeout? (because of https
>    traffic, session ticket etc)
> Thanks in advance!
> --
> Cheers,
> Abhijeet (

Abhijeet (
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