Antecedentes Nacionales

You need to create a network object for every server in the server farm. You do this by clicking Manage  Network Objects to access the Network Objects Manager. Then, click New  Node  Host to bring up the Host Node General Properties screen, shown in Figure 3.10.

You identify each object by typing in a name and the IP address of the server and then clicking OK.

120 Chapter 3 ^ Load Balancing

F I G U R E 3 . 1 0 Creating a Workstation/Host Node object

Some NG FP1 object names have changed significantly in NG FP2. Depending on which version of NG you are running, you could be creating a new Work-station object (as defined in FP1) or a new Host Node object (as defined in FP2).

Object names didn’t change much between FP2 and FP3, but the names of all the GUIs did.

Naming these objects similarly will make identification easier. For example, you might use the names HTTP1, HTTP2, HTTP3, and so on. Because the Objects Tree organizes names alphabetically, the objects will be listed together.

After you create a Host Node object for every server in the server farm, you need to pull the objects into a group object. You do so through the Net-work Objects Manager. Create a new group by clicking New  Group  Simple Group, which brings up the Group Properties dialog box shown in Figure 3.11.

Implementing Load Balancing 121

F I G U R E 3 . 1 1 Creating a server group

The name of the group should correspond to the names of the Host Node objects you created (for example, HTTP_Group). This approach keeps your naming convention consistent and makes it easy to identify which servers belong to which group. The Comment and Color fields are optional. The Host Node objects created should be listed in the left column. Select the objects that represent the servers in the server farm (by holding down the Ctrl key and clicking each one) and add them to the In Group column on the right by click-ing the Add button.

The next task is to create the logical server object. This object represents the routable IP address that will be published (via DNS) to the whole world as your server IP address.

There are a few ways to create this object. You can go to the menu bar and select Manage  Network Objects, and then select New  Logical Server in the Network Objects Manager—but that’s a lot of steps. We prefer to use the new Objects Tree to create objects. Figure 3.12 shows this process, which you can use to create most objects.

122 Chapter 3 ^ Load Balancing

F I G U R E 3 . 1 2 Creating a logical server object from the Objects Tree

You can create most objects from the Objects Tree, not just logical server objects.

When you right-click on Logical Server and select New Logical Server, the Logical Server Properties window appears as shown in Figure 3.13. Enter a name in the Name field and the routable IP address in the IP Address field.

Again, follow the same naming convention you started earlier. The IP address is the DNS-resolvable valid IP address registered in the public DNS, such as 172.21.101.100. Your firewall address is 172.21.101.1, but your web traffic has the address of 172.21.101.100. Any traffic to the firewall on 172.21.101.1 is dropped by the stealth rule, but traffic to the logical servers’

IP address of 172.21.101.100 is accepted. The Comment and Color fields are not required, but they’re a nice way to organize your objects.

F I G U R E 3 . 1 3 Logical Server Properties window

Next, select the Server’s Type option. Select HTTP if you are load-balanc-ing web servers. If you are usload-balanc-ing valid routable addresses for the servers in your server farm or if you do not care if the actual IP addresses of the load-balanced servers are known, then HTTP is the proper choice. For every other TCP protocol, select Other. You can use Other for HTTP traffic as well, if you wish to hide the true IP addresses of the servers in your server farm.

Persistent Server Mode should always be turned on. This option is the

“superglue” of the logical server: It makes the connection stay with the same server or service for a time frame specified by you in the Global Properties.

Persistent Server Mode is helpful with services such as FTP , which involve an active connection. You want the connection to stay with the same server throughout the duration of the session. That way, if there is a break in the session, you will be able to get back to that specific server to complete the download. With Persistent Server Mode turned on (it is on by default), two persistency options are available: You can choose to make the connection persistent based on either the service being used (HTTP, FTP, and so on) or the server selected by the algorithm.

If a client adds the URL of one of the load-balanced web servers to their browser’s Favorites list and HTTP was the Server’s Type method chosen, the URL reflects the true IP address of the web server. However, if the Other method was chosen, the client is really adding the URL of the logical server IP address, even if this is done after the load balancing has taken effect. This happens because Persistent Server Mode is active for each session. When the client clicks on an item in the Favorites list, a new session is created; this new session is directed to one of the servers in the server farm based on the selected algorithm.

Finally, you select the Balance Method from the five algorithm options described earlier in this chapter. You can see what a completed logical server object looks like in Figure 3.14.

F I G U R E 3 . 1 4 Completed logical server object