[ClusterLabs] newbie question

[Ken Gaillot]

On 05/05/2017 03:09 PM, Sergei Gerasenko wrote:
> Hi,
> 
> I have a very simple question. 
> 
> Pacemaker uses a dedicated "multicast" interface for the totem protocol.
> I'm using pacemaker with LVS to provide HA load balancing. LVS uses
> multicast interfaces to sync the status of TCP connections if a failover
> occurs.
> 
> I can understand services using the same interface if ports are used.
> That way you can get a socket (ip + port). But there's no ports in this
> case. So how can two services exchange messages without specifying
> ports? I guess that's somehow related to multicast, but how exactly I
> don't get.
> 
> Can somebody point me to a primer on this topic?
> 
> Thanks,
>   S.

Corosync is actually the cluster component that can use multicast, and
it does use a specific port on a specific address. By default, it uses
ports 5404 and 5405 when using multicast. See the corosync.conf(5) man
page for mcastaddr and mcastport. Also see the transport option;
corosync can be configured to use UDP unicast rather than multicast.

I don't remember much about LVS, but I would guess it's the same -- it's
probably just using a default port if not specified in the config.