On 29 Dec 2014, at 12:13, Ben Langfeld <ben@langfeld.co.uk> wrote:

On 27 December 2014 at 23:44, Carsten Bock <carsten@ng-voice.com> wrote:
Hi Mahmoud,

Thy typical way, to build a Active/Active setup is by using DNS-SRV
records. The two servers get different IPs and you announce both IPs
using DNS to the devices. Most common User-Agents support this
nowadays, so that's kind of easy. It is specified in RFC3263:
"Locating SIP-Servers" (http://tools.ietf.org/html/rfc3263).

However, when using DNS-SRV records, dialogs and transactions are
still associated with a single server, even though the User-Agent has
an Alternative, in case one server fails. If you want to increase the
HA for this, you can advertise the Domain name instead of an IP
(causes more DNS-Lookups).

Just a word of caution here, there are several SIP stacks which don't handle SRV lookups correctly. I don't mean to discourage you from this, but just to be aware of it. For example, Mobicents only understands SRV record sets which return domain names. If you return IPs, Mobicents will go ahead and look them up as A records and fail.

RFC 2782 says that the target has to be a name which you look up in the next step. I'm not clear that a name
can't be an IP address, but there's no example of that. It's an interesting question. I see no reason for adding
IP addresses there though.

Asterisk fails miserably in DNS SRV support. Been working on fixing that for chan_sip for a while, but
the DNS code is really bad and hard to clean up. 

/O
 
You can share the dialog state etween two nodes by using the dialog
module in db-only mode (db_mode = 1, see
http://kamailio.org/docs/modules/devel/modules/dialog.html#idp15368320).
You cannot share transactions between two nodes, only dialogs.

In addition, you can work with virtual IPs with Heartbeat/Pacemaker.

At a big operator, we've used a combination of the two: Active/Passive
for one site and DNS-SRV to distribute it among different sites.

Kind regards,
Carsten

2014-12-26 19:07 GMT+01:00 Mahmoud Ramadan Ali <cisco.and.more.blog@gmail.com>:
> Hi Dears,
> I have successfully configured Kamailio HA using Heartbeat and Pacemaker so
> if one of the two servers should go down the other server will own the
> virtual IP address and take over.
> But i have two questions:
>
> 1.This model is considered to be Active / Passive redundancy so one server
> will process the SIP signaling until it goes down and i'm wondering is there
> is any way two achieve Active / Active redundancy and if so how the
> signaling will be handled on the servers so they can be aware of the
> transactions and dialogs traversing the servers ? does the signalling will
> be replicated or synchronized between the servers or what ?!
>
> 2.What about the servers DB and how they should be designed in a cluster
> mode ? i want to replicate all the DBs of the server to get consistent user
> registration using the subscriber table for example.
>
> Thanks in advance and Best regards.
>
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