[sr-dev] Proposed Change to DMQ Notification Address Resolution

[Charles Chance]

Hello Bob,

As previously stated, it is a needed improvement.

My time is heavily consumed right now, so your patch will be gratefully
received.

My only comment would be that once connected to the cluster, notifications
are sent to all nodes anyway, not just the one specified in the
notification address parameter. So practically, the only need for resolving
multiple records is on start-up to find the first available node. Upon
contact with that node, a list of the other nodes is returned, all of which
are stored and included in subsequent notifications - this is fairly
fault-tolerant, providing your network is well designed. It is not tolerant
of network splits etc, where it could be possible to end up with two or
more separated clusters or split-brain type situations. However, to
overcome that, I think we're looking at a *major* redesign - far more than
can be achieved with multiple notification addresses. We'd also likely need
to consider quorum, voting a primary/master etc. to do it properly.

Otherwise, it is a welcome addition in my opinion.

Cheers,

Charles


On 5 March 2015 at 21:41, Robert Boisvert <rdboisvert at gmail.com> wrote:

> DMQ Developers,
>
> Our team would like to setup a DMQ bus
> <http://kamailio.org/docs/modules/4.2.x/modules/dmq.html#idp2640048> that
> contains more than one notification address
> <http://kamailio.org/docs/modules/4.2.x/modules/dmq.html#dmq.p.notification_address>
> to support a high availability, fault-tolerant system where multiple
> servers are used to maintain the list of DMQ nodes.  The failure of any one
> DMQ node or the startup order should not cause the DMQ bus to lose track of
> available nodes.  As nodes go offline and online the DMQ bus should be
> updated using information from the active nodes.   To do this we propose
> changing the way DMQ uses the notification address.
>
> Currently the notification address resolves a DNS name to a single IP
> address even if a SRV record or multiple A/AAAA records are available.  The
> proposal is to use all the A/AAAA records or SRV targets returned from a
> DNS name query as notification addresses.
>
> Do you have any comments, concerns, suggestions, or recommendations
> regarding this proposal?  Your input is definitely welcome.
>
> Thank you,
> Bob
>
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>

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