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

To: Julian Anastasov <ja@xxxxxx>
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: yangxingwu <xingwu.yang@xxxxxxxxx>
Date: Thu, 28 Oct 2021 10:50:00 +0800

On Thu, Oct 28, 2021 at 5:09 AM Julian Anastasov <ja@xxxxxx> wrote:
>         Hello,
> 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 is we can NOT decide what the customers do, many of them
run kubernetes with old versions of kube-proxy. And most importantly,
upgrade to new version is a very long and painful process, that's why
we want to fix this at the kernel level

>         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.

ok, got it, I will try to fix this problem

> Regards
> --
> Julian Anastasov <ja@xxxxxx>

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