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

[yangxingwu <xingwu.yang@gmail.com>]

thanks Julian

yes, I know that the one-second delay issue has been fixed by commit
f0a5e4d7a594e0fe237d3dfafb069bb82f80f42f if we set conn_reuse_mode to
1

BUT  it's still NOT what we expected with sysctl settings
(conn_reuse_mode == 0 && expire_nodest_conn == 1).

We run kubernetes in extremely diverse environments and this issue
happens a lot.

On Tue, Oct 26, 2021 at 1:44 PM Julian Anastasov <ja@ssi.bg> wrote:
>
>
>         Hello,
>
> On Tue, 26 Oct 2021, yangxingwu wrote:
>
> > thanks julian
> >
> > What happens in this situation is that if we set the wait of the
> > realserver to 0 and do NOT remove the weight zero realserver with
> > sysctl settings (conn_reuse_mode == 0 && expire_nodest_conn == 1), and
> > the client reuses its source ports, the kernel will constantly
> > reuse connections and send the traffic to the weight 0 realserver.
>
>         Yes, this is expected when conn_reuse_mode=0.
>
> > you may check the details from
> > https://github.com/kubernetes/kubernetes/issues/81775
>
>         What happens if you try conn_reuse_mode=1? The
> one-second delay in previous kernels should be corrected with
>
> commit f0a5e4d7a594e0fe237d3dfafb069bb82f80f42f
> Date:   Wed Jul 1 18:17:19 2020 +0300
>
>     ipvs: allow connection reuse for unconfirmed conntrack
>
> > On Tue, Oct 26, 2021 at 2:12 AM Julian Anastasov <ja@ssi.bg> wrote:
> > >
> > > On Mon, 25 Oct 2021, yangxingwu wrote:
> > >
> > > > Since commit dc7b3eb900aa ("ipvs: Fix reuse connection if real server is
> > > > dead"), new connections to dead servers are redistributed immediately to
> > > > new servers.
> > > >
> > > > Then commit d752c3645717 ("ipvs: allow rescheduling of new connections when
> > > > port reuse is detected") disable expire_nodest_conn if conn_reuse_mode is
> > > > 0. And new connection may be distributed to a real server with weight 0.
> > >
> > >         Your change does not look correct to me. At the time
> > > expire_nodest_conn was created, it was not checked when
> > > weight is 0. At different places different terms are used
> > > but in short, we have two independent states for real server:
> > >
> > > - inhibited: weight=0 and no new connections should be served,
> > >         packets for existing connections can be routed to server
> > >         if it is still available and packets are not dropped
> > >         by expire_nodest_conn.
> > >         The new feature is that port reuse detection can
> > >         redirect the new TCP connection into a new IPVS conn and
> > >         to expire the existing cp/ct.
> > >
> > > - unavailable (!IP_VS_DEST_F_AVAILABLE): server is removed,
> > >         can be temporary, drop traffic for existing connections
> > >         but on expire_nodest_conn we can select different server
> > >
> > >         The new conn_reuse_mode flag allows port reuse to
> > > be detected. Only then expire_nodest_conn has the
> > > opportunity with commit dc7b3eb900aa to check weight=0
> > > and to consider the old traffic as finished. If a new
> > > server is selected, any retrans from previous connection
> > > would be considered as part from the new connection. It
> > > is a rapid way to switch server without checking with
> > > is_new_conn_expected() because we can not have many
> > > conns/conntracks to different servers.
>
> Regards
>
> --
> Julian Anastasov <ja@ssi.bg>