Clustering enterprise application servers from Macromedia with Alteon''s ACEdirector Switch

Alteon's ACEdirector switch is rich with capabilities. This article sorts through the vast variety of possible switch configurations and defines setup parameters best suited to the needs of most Macromedia enterprise server customers. It describes a basic procedure resulting in a server farm running ColdFusion or JRun behind an ACEdirector (AD3).

Frank DeRienzo, MBA, MCSE

Principal Technical Support Engineer

Macromedia, Inc.

The AD3 will manage session traffic through a virtual server. The AD3 virtual server will associate with each Web/application server in the farm; AD3 will monitor the health of each Web/application server in the farm and distribute session load accordingly. ClusterCATS (CC) will provide probes that proactively monitor the health of any web server: NES, IIS, or Apache. It will also monitor JRun or ColdFusion. If either the Web server or application server hangs, CC will kick the server back up and send out status alerts via E-mail. The combination of CC and AD3 presents a paradigm for Web site resiliency.

Note: If you are running ColdFusion 5, instead of clustering, you may wish to use the Server Monitoring option with AD3. ColdFusion 5 Server Monitoring provides all the server level capabilities of CC without the overhead of a cluster.

Note also: If you wish to set up your server farm in distributed mode (DM) by separating your Web servers and your application servers onto different systems, go to the Macromedia Support Center and search on the key word distributed. The articles which appear will provide procedures and recommendations for configuring a distributed mode server farm. You will also find distributed mode referenced under the Designer and Developer link on the Macromedia home page.

To enhance clarity and simplicity, this article is example-based. Consider the following example of a two-server cluster. Picture two server-class systems - tiger-one.macromedia.com and tiger-two.macromedia.com - configured in a passive-mode cluster using private IP addresses 192.168.64.11& 12. A third IP address, 192.168.64.1, will be used on the AD3 to provide a default gateway for the server farm. The fourth address 10.64.20.93 is for the virtual server on the AD3; this address corresponds in DNS to the name that your browsing customers will place in the URL line. It represents a public address. The fifth, 10.64.20.96, will be used for administration of the AD3.

I use private, internal addresses for the Web/application servers, because only the Alteon VIP address needs to be public. Public IP addresses tend to be rare these days.

The example list of names and IP addresses that follows is an illustration of the hosts file that you will need to place on each server in the farm. On an NT server, the hosts file resides in \winnt\system32\drivers\etc. On Solaris or Linux, it resides in /etc. Before going on to the next step, use your favorite text editor to create and place the hosts files on the appropriate servers in the farm: tiger-one and tiger-two. Do not forget to configure the default gateway on each server.

Note: This example is based on using Macromedia enterprise application servers ColdFusion or JRun with AD3 software version 8.0.60.7. If you need to upgrade your AD3, contact Alteon technical support. I found Alteon's binary upgrade procedure to be very simple and fast.

A.) Place the two CF/JR Web servers into a passive-mode CC cluster behind the AD3. You must use static Web site IP addresses; CC failover (high-availability) must be turned off. During CF/JR installation, select no server failover. If you are running NT 4.0, do not set up your Web servers with dynamic IP addresses. AD3 will be providing failover services. Dynamic IP addressing is only used with CC's implementation of failover on NT. If you are adding AD3 to a ColdFusion and CC cluster that is already set up with dynamic Web site IP addresses on NT 4.0, you must switch to static Web site IP addresses and disable CC failover.

B.) Let's begin to configure the AD3, and then we will go back to the clustered server farm. This example-based article is designed as a CF/JR supplement to your AD3 documentation. Use this procedure along with your Alteon documentation incorporating the following supplemental modifications illustrated using the Web servers from our example and using an AD3 virtual server address (VIP) of 10.64.20.93:

C.) Now it is time to turn back to the clustered real server farm. Open the CC Explorer on tiger-one and select your cluster: Start > Programs > ClusterCATS > ClusterCATS Explorer > Right-click on a cluster and select > Properties > Load-Balance > Load-Balancing Product > Other.

D.) If you are running ColdFusion, configure the cfprobe.cfm to record application awareness. Edit cfprobe.cfm in the cfusion\brighttiger\btauxdir using a simple text editor such as Notepad in such a way that ColdFusion is used to provide output. When properly configured using cfprobe.cfm as the target page, AD3 will detect failure of an application server. In all tests, the AD3 keepalive uri was pointed at cfprobe.cfm or jrunprobe.jsp along with the CC probe.

Note: If you are running JRun, there is no need to edit the jrunprobe.jsp page; it is already application aware.

E.) Now that your cluster is up and running, you are ready to configure the AD3 for CF/JR content and application awareness health checking. This will enable the AD3 to properly recognize and react to any disruption of service in the real server farm. This is a critical step especially if you are running your server farm in distributed mode with the Web servers set up on separate platforms from your application servers. It is not hard to picture your AD3 pouring sessions onto a Web server that has a stalled backend application server. What would tell the AD3 that the application server behind the Web server was down?

Health checking is the answer. Health check scripts are probably the most complex aspect of this procedure (if not the most complex thing to set up on the AD3). I will set up the health script to look at the cfprobe.cfm or jrunprobe.jsp and look for the return string of "Hello" (which, after the previous step is now generated by the application server rather than simply plain text). If an application server is down, the AD3 will not get back the "Hello" message and will mark the appropriate server(s) down while redirecting request to the server(s) that remain(s) alive.

Note: These strings are case sensitive and this first example checks the health of a JRun application server.

The most complicated piece of the health check script is the send line. Depending on how you view this article, it may appear that the send line is broken into two commands but it is not. Be careful when printing this article, some printers will cut off the end of the send line:

For JRun use:

For ColdFusion use:

Health check scripts on the AD3 are as complex as they are important. In order for the script to work against ColdFusion code, you must make sure that the hosts file on each real server in the farm is complete to include the AD3 virtual server (in our example 10.64.20.93). The default gateway on the private side of the AD3 (in our example 192.168.64.1) must also be configured on each real server in the farm.

Another tricky AD3 entry is the health check typescript1, you will notice that when you change the health check type of the group from tcp to the script there is not a space between the word script and the number 1. This is inconsistent with the rest of the AD3 commands, but the script check will not supercede the default tcp check if you put in a space.

This concludes the article. The result of following this workaround procedure is a ColdFusion or JRun cluster running behind an AD3 with CC monitoring CF/JR and IIS (or NES or Apache) availability. This provides Web server recovery in the event of a hang or crash, automatic E-mail alerts for Web server problems, and daily server status reports. There is much more you can accomplish by combining ACEdirector with Macromedia's enterprise application servers. For example, you may choose to set up numerous geographically distributed CF/JR Web sites using ACEdirector's Global Server Load Balancing feature. ACEdirector is a high-end switch; when combined with a cluster of Macromedia's enterprise application servers, the end result is a world-class Web site.