Clustering for 120 seats

[mumin37]

Hi,

First of all I want to tell, that I've got a little bit of experience with ViciDial (ViciBox installations). I know, there is information in ViciBox's manual about clustering and servers requirements, but it's not so obvious for me. Let me explain.

When I've installed single server for ~50 Agents (outbound only) on Dell 1950 (2x Quad Core 2.4GHz, 16 GB RAM, 2 SCSI disks - Raid 1) it worked very fine for 40+ agents. Load average was between 0.2-1.5 (depended on Ratio/Adapt level). load average 0.2 was when adapt level was ~2, 1.5 when ratio ~5. No one call was bad quality etc.

I had only one issue when Load average grown to 15.0 - when my VoIP provider had a choke and was disconnecting all calls. Then Vicidial tried to queue all calls trying to ring, so there were also tons of queries to MySQL.

But it was my old scenario. Now I'd like to have 120 seats in CallCenter and I'm wondering if I can do this installation on 2 servers only, just because I don't have too much money to buy 4 strong machines. Maybe there is... let's call it "performance key", which gives Asterisk machines a lot of power - like 32 or 64 GB RAM instead of 16. Or maybe Ethernet Load Balancing is important? Or SSD disks (for DB and Asterisk). Maybe someone tried to do this.

Can anyone explain me, what is Achilles heel in Single Server installations (not including possibility of failures)? Is that RAM, Disks, Ethernet or Processors?

Thanks in advance for explanations and possible discussion.

[Rudolfmdlt]

Hi Mimin37,

Asterisk has an inherent limit of about 200 sessions/channels (Please correct me if I am wrong). So if you are dialing 3:1 with 50 agents, there are 50 sessions taken up by the agents and another 150 for the 3:1 dialing (In theory). So at a Max, you could do 3:1 with 50 agents on 1 dialer - this is not recommended and if you search around you will see the manuals and many forums posts state this; 20-25 agents per dialer.

I would spend money on a proper DB server, the manuals spec these clearly, and save on hardware for the dialers. Your dialers do not need to be powerful at all.

I hope this answers your question.

Rudolf

[gardo]

Not really a hard limit. We have made over 700 simultaneous calls in a single Asterisk server. The Vicidial group has also made more than that. The problem with Asterisk is that the higher the number of channels, the less stable it gets. So it's best to keep it an optimal level to maintain stability (depends on your setup).

You can have more than 100 agents on 1 server in a Vicidial cluster. There is really no 20-25 agents per dialer.

The major bottleneck in a single server system is the harddrive IO. Specially if you're using traditional (spinning) harddrives (SATA and SAS) doing full recordings on all calls and doing queries on the database. As @Rudolfmdlt said, it's best to have a separate proper DB server and dialers.

[tick]

Yes, gardo is right.
And when you record all calls then is a big problem especially if you are doing compressions. So always seperate DB and dialer even if you use "pure asterisk".

[Vince-0]

Your RAID1 is probably a bottleneck on the DB queries. Check using " iostat -x 1 " for %util and wait to see if the disks are choking trying to fulfil DB queries.

Vin.

[mumin37]

So, best solution would be RAID 10 on SSD Disks. Then queries should be very, very fast.
I think I'm gonna try to install MySQL also in another subnet for better network performance. Is it good practice?

[Vince-0]

RAID10 is advisable on SAS. I don't think SSD disks are required because you will see a MySQL service bottleneck before the disks start slowing queries down. The MySQL server shouldn't be on a different subnet for any reasons, keep all Vici servers on the same switch.

[gardo]

If money is of no consequence then get the best hardware available. Specially SSDs. Though there really is no need for RAID10 SSDs since SSDs are already blazingly fast (we get around 500+ MB/S write speed consistently - using Samsung 512 GB SSD) and durable. But if you want overkill then go for it.

[mumin37]

Vince-O,

Sorry, but I can't see any reason why db server shouldn't be on different subnet.

If I do a connection like that:

Asterisk/Web server:
eth0 (192.168.0.0/24) - connection to "real network" with computers etc.
eth1 (10.0.1.0/24)- connection to MySQL server (ommiting switch), direct connection between servers, no routing between subnets.

Mysql Server:
Eth0 - connection to Asterisk/Web server, no internet, no connection to 192.168.0.0

If so, I think, that would be ok. For security reasons, network speed and others. If there are reasons why I shouldn't do that way, please list it.