[rabbitmq-discuss] Federation connections, VIPs, and queues

Matt Pietrek mpietrek at skytap.com
Wed Dec 12 17:06:23 GMT 2012

Ping on this question - My guess it that it just got lost in the shuffle.

Also, just realized in the above question that I transposed something. The
two lines that say:

federation: skytap -> rabbit at slave
federation: skytap -> rabbit at slave-alternate

Should instead be:

federation: skytap -> rabbit at master
federation: skytap -> rabbit at master-alternate



On Mon, Dec 10, 2012 at 1:17 PM, Matt Pietrek <mpietrek at skytap.com> wrote:

> I realize this is a somewhat esoteric question and apologize for the
> complexity. We're still on 2.8.7 for a while, although my guess is that
> federation in 3.0 won't drastically change the answer.
> In our setup, we have bidirectionally federated nodes, i.e.  'slave' <->
> 'master' with an exchange named 'skytap'.  To this mix I add a set of
> alternate nodes to enable non-stopping upgrades: 'master-alternate' and
> 'slave-alternate'. The primary and alternate nodes are identically
> configured.
> I'm using VIPs (keepalive based) for connections between nodes. There's a
> vip-master and a vip-slave. Most of the time vip-master points at the
> 'master" node, but occasionally points at the 'master-alternate" node. In
> the rabbitmq.config, I specify the VIP names everywhere (i.e vip-master,
> vip-alternate), and never mention the actual node names.
> When I first start this up, I see a federation support queue like this:
> federation: skytap -> rabbit at master
> This is what I'd expect based on my understanding of federation.
> However, after doing an upgrade process (i.e., vip-master goes from
> 'master' to 'master-alternate' and back to 'master'), I have two queues now:
> federation: skytap -> rabbit at slave
> federation: skytap -> rabbit at slave-alternate
> This isn't so good. The vast majority of the time the slave-alternate node
> isn't around. Messages sent to the skytap exchange just pile up in the
> second queue. (The do of course get delivered to the non-alternate slave
> node.)
> *Question 1:*
> I'm trying to understand this behavior. It's almost as if the federation
> logic is burrowing underneath my VIP and discovering the actual node names.
> In my naive understanding, I'd expect that the use of VIPs would hide away
> the primary/alternate nodes.
> That said, I do notice in the connections list that incoming connections
> come from the 'regular' node IP, not from the VIP that's assigned to the
> same node. Not sure if this is relevant or not.
> *Question 2:*
> In a related vein, looking at the Exchanges I see exchanges like this:
> federation: skytap -> rabbit at slave A
> federation: skytap -> rabbit at slave-alternate B
> What do the A/B signify?
> Thanks,
> Matt
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