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From Keith W <keith.w...@gmail.com>
Subject Re: Broker-J HA with just 2 brokers
Date Wed, 24 Jan 2018 09:37:18 GMT
Hello Bryan

Broker-J does support a active/passive groups formed of two nodes.

In a two node group, both nodes to be online in order to maintain
quorum.    If one node were to fail business will stop. In order to
restore service from a single node, a 3rd party (script and/or human)
needs to intervene and set "Allow to Operate Solo" on the surviving
node.  This overrides the normal quorum requirement and allows service
continue from the one.   It is important to manage the setting of
"Allow to Operate Solo" carefully. If you were to set it on both nodes
and the network link between the two nodes be lost both nodes would
become master and process transactions independently (i.e.a  split
brain).  Read more here:

https://qpid.apache.org/releases/qpid-broker-j-7.0.0/book/Java-Broker-High-Availability-OverviewOfHA.html
https://qpid.apache.org/releases/qpid-broker-j-7.0.0/book/Java-Broker-High-Availability-Behaviour.html

"Required Minimum Number Of Nodes" actually applies to groups of three
or more.  It has no effect on a two node group (and is hidden from the
UI when  two node group is configured).  It is used to reduce the
quorum requirement in groups of three or more allows service to be
restored in extraordinary failure scenarios.  Obviously the same care
needs to be taken with this setting to avoid the possibility of
split-brain.

Whilst it is technically possible to host a group of three nodes
across two JVMs, you defeat the purpose of a three node group - the
ability to recover -automatically- from a single node failure.

Hope this helps.

Keith


On 23 January 2018 at 20:23, bryand <bryan@bldixon.net> wrote:
> I'm just getting started with QPid and want to setup HA with Broker-J.  We
> are trying to replace our current ActiveMQ environment where we use a Master
> Slave approach for HA and just have 2 nodes running.  I really want to just
> have 2 nodes with Broker-J also because that setup has been working fine for
> us with ActiveMQ and I really don't want to have 3 VMs used for both our
> Test and Production Broker-J environments.
>
> I've read the documentation regarding Required Minimum Number Of Nodes and
> Allow to Operate Solo and it sounds as if those options are really meant for
> manual use in a 2 node HA environment (for example you shouldn't have Allow
> to Operate Solo enabled for more than one node at a time).
>
> Is it possible to have a 3 node environment just using 2 brokers (so I can
> just have 2 VMs for each of our Test and Production environments)?  For
> example can I have one VirtualHostNode on Broker A and then 2
> VirtualHostNodes on Broker B.  I've set this up but am not having much luck
> getting either node on Broker B accept requests from a client (when I stop
> the node on Broker A) even though the Virtual Host is reporting as ACTIVE on
> Broker B - the client is reporting that the Virtual Host is unknown.
> However as soon as I start the Virtual Host Node on Broker A, I can
> successfully have my (JMS) client connect to the MASTER Virtual Host Node on
> Broker B.
>
> Anyway I'm wondering if the setup I'm trying (2 VMs with 1 Broker running on
> each but 1 of the brokers has 2 VirtualHostNodes for the VirtualHost) is
> even valid or do I really need to have 3 VMs with 1 Broker each running?
> Just trying to see if I can keep the same 2 VM setup we have for ActiveMQ.
>
>
>
> --
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