Re: [PATCH] ipvs: Fix reuse connection if RS weight is 0

To: yangxingwu <xingwu.yang@xxxxxxxxx>
Subject: Re: [PATCH] ipvs: Fix reuse connection if RS weight is 0
Cc: Simon Horman <horms@xxxxxxxxxxxx>, netdev@xxxxxxxxxxxxxxx, lvs-devel@xxxxxxxxxxxxxxx, netfilter-devel@xxxxxxxxxxxxxxx, linux-kernel <linux-kernel@xxxxxxxxxxxxxxx>, linux-doc@xxxxxxxxxxxxxxx
From: Julian Anastasov <ja@xxxxxx>
Date: Thu, 28 Oct 2021 00:09:09 +0300 (EEST)

On Wed, 27 Oct 2021, yangxingwu wrote:

> what we want is if RS weight is 0, then no new connections should be
> served even if conn_reuse_mode is 0, just as commit dc7b3eb900aa
> ("ipvs: Fix reuse connection if real server is
> dead") trying to do
> Pls let me know if there are any other issues of concern

        My concern is with the behaviour people expect
from each sysctl var: conn_reuse_mode decides if port reuse
is considered for rescheduling and expire_nodest_conn
should have priority only for unavailable servers (nodest means
No Destination), not in this case.

        We don't know how people use the conn_reuse_mode=0
mode, one may bind to a local port and try to send multiple
connections in a row with the hope they will go to same real
server, i.e. as part from same "session", even while weight=0.
If they do not want such behaviour (99% of the cases), they
will use the default conn_reuse_mode=1. OTOH, you have different
expectations for mode 0, not sure why but you do not want to use
the default mode=1 which is safer to use. May be the setups
forget to stay with conn_reuse_mode=1 on kernels 5.9+ and
set the var to 0 ?

        The problem with mentioned commit dc7b3eb900aa is that
it breaks FTP and persistent connections while the goal of
weight=0 is graceful inhibition of the server. We made
the mistake to add priority for expire_nodest_conn when weight=0.
This can be fixed with a !cp->control check. We do not want
expire_nodest_conn to kill every connection during the
graceful period.


Julian Anastasov <ja@xxxxxx>

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