Re: [lvs-users] Sync issue after master reboot

To: Julian Anastasov <ja@xxxxxx>
Subject: Re: [lvs-users] Sync issue after master reboot
Cc: "lvs-users@xxxxxxxxxxxxxxxxxxxxxx" <lvs-users@xxxxxxxxxxxxxxxxxxxxxx>
From: "Markhasin, Dan" <dan.markhasin@xxxxxxxxx>
Date: Tue, 25 Feb 2014 13:03:04 +0000
Thanks for the reply.

Let me clarify, it doesn't stop synchronizing information after the reboot. The 
synchronization continues, but after the old master is rebooted its connections 
table is obviously wiped clean.
At this point, the old slave (now acting as master) has a full connections 
table, and new connects are being synchronized with the old master, but only 
the *new* connections are synchronized. Connections that existed on the slave 
before the master failed will not be synchronized, and if I initiate failback, 
they will be disconnected.

Is this clearer now? :)


-----Original Message-----
From: Julian Anastasov [mailto:ja@xxxxxx] 
Sent: Tuesday, February 25, 2014 10:26 AM
To: Markhasin, Dan
Cc: lvs-users@xxxxxxxxxxxxxxxxxxxxxx
Subject: Re: [lvs-users] Sync issue after master reboot


On Wed, 12 Feb 2014, Markhasin, Dan wrote:

> Hello,
> We are currently building an LVS cluster with two ldirector servers to ensure 
> HA. Each of these servers has two ipvsadm 1.26 sync daemons running, which we 
> start by:
> On master:
> --start-daemon master --syncid 50
> --start-daemon backup --syncid 51
> On backup:
> --start-daemon master --syncid 51
> --start-daemon backup --syncid 50
> During normal operation there are no issues, connections are made to the 
> master and are synced to the backup. In case the master goes down, the 
> connections seamlessly transfer over to the backup.
> However, in the case of a reboot of the master, after the master is brought 
> back online and the ipvsadm daemons are started, the existing connections 
> from the backup server are not synced to the master - causing them all to 
> disconnect whenever a failback is performed. New connections made to the 
> slave are synced, but the old ones are not.
> I have seen references from the past decade to this problem, but have found 
> no solution for syncing the master and the backup server after the master's 
> reboot. Any help would be greatly appreciated!

        Yes, there is no trigger implemented to sync all
connections at once. But looking at the code I don't see
why sync should stop transferring information. I don't
know what kernel you are using but even connections with
IP_VS_CONN_F_SYNC bit (created while we were backup)
should be synced when we are master. Of course, it can depend
on forwarding methods, fwmark usage, kernel (IPVS sync
protocol) version, netfilter (stateful firewalling dropping
the synced conns), etc. May be you can give more information
and to share more observations.


Julian Anastasov <ja@xxxxxx>
Intel Israel (74) Limited

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