Question about placement of Web Dialer Service in cluster

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Feb 15th, 2010
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I have a cluster of 6 servers on I'd like to use the Click to Call widget, and need to enable and configure the Web Dialer Service. My question is around the placement of the service - or, which of my servers should I enable it on? No.1 is my pub, 2,3, and 4 are my subs followed by 5 and 6 as my TFTP etc.

My guess is that I should enable the service on my subs (2, 3, and 4), because these are the servers that users' phones will be registered to.

I'd appreciate any guidance anyone can offer.



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William Bell Mon, 02/15/2010 - 16:56
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I recommend enabling Web Dialer on the call processing subscribers in your cluster.  I assume from your intro you are doing a 2:1 redundancy model in your call processing.  So, you should enabled it on one of your primary call processing nodes and the backup call processing node.  If you want to have the service configured on multiple primary nodes for load balancing reasons than you can do that.  Just keep in mind that the Web Dialer interface relies on the CTIManager services.  So, make sure that the service parameters of Web Dialer (where you define the CTI servers) line up with your design objectives.

Secondly, your clients need to "point" to a Web Dialer service.  I don't recall if the Click-to-Call application provides a way for you to define a "secondary" WebDialer service or not.  If not, then you will need to keep in mind that the Web Dialer SOAP interface (which I believe is used by Click-to-Call) is essentially a web service.  If you can only assign one web dialer service to the Click-to-Call client then you still have a single point of failure regardless of how many CUCM nodes are configured to run the WebDialer service.   As with other web enabled interfaces (APIs or XML apps) in a UC solution, you will want to look at a way to provide redundancy for the fundamental client connections.

One method is using the SLB feature in IOS or Cisco ACE.  Another method is using DNS A records.

Method 1 example:

DNS name of webdialer service:

- The A record points to a virtual IP on a SLB capable device

- The VIP on the device points to the webdialer servers in your cluster

Method 2 example

Two records in DNS.  (for example)  3600  IN A  3600  IN A

Basically, you would be using DNS for redundancy.  The problem is that for applications like click to call this is essentially useless as loss of one server could mean a 30 to 45 second (or more) delay in establishing the SOAP transaction.

Anyway, the point is that enabling Web Dialer on a bunch of servers in the cluster isn't enough if you are considering redundancy of this application as critical from an operational perspective.

Hope this helps.



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