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You can configure the ServerIron ADX to distribute SLB traffic among GSLB sites based on weights configured for the sites. The weights determine the percentage of traffic each site will receive in comparison with other sites, which may or may not have weights.
NOTE
You cannot use the Weighted Site metric if the Weighted IP metric is enabled.
NOTE
The main criteria for the Weighted Site metric is that the total number of times the GSLB selects each domain-IP for the client request is in proportion to the relative site weights.
You assign weights to GSLB sites. Each GSLB site may consist of one or more ServerIron ADXs, but the weight is applicable to the site as a whole.
The GSLB ServerIron ADX uses relative percentages in order to achieve 100% total weight distribution, as shown in Table 5 and Table 6. In Table 5, the total of the Configured Weighted Site metrics (2nd column) is 100. The last column shows that the GSLB ServerIron ADX distributes the traffic to the IP addresses exactly as configured. In this example, traffic distribution is
straightforward because the total weight of all three GSLB sites equals 100.
Now consider the example in Table 6. In this example, the total of the Configured Weighted Site metrics (2nd column) does not equal 100. However, as illustrated in the last column, the GSLB ServerIron ADX uses relative percentages in order to achieve 100% total weight distribution.
By default, the Weighted Site metric is disabled. When enabled, it is placed second in the GSLB algorithm, after the Health Check metric. You can change the metric order and enable or disable other metrics, although we do not recommend this. For more information, refer to “Changing the order of GSLB policy metrics” on page 38.
DNS response processing
When the Weighted Site metric is enabled, the GSLB ServerIron ADX selects an IP address belonging to a particular site to be the best IP address in the DNS reply to a client. The client subsequently makes an SLB request to that IP address.
TABLE 5 Example Weighted Site metric configuration
GSLB site Configured Weighted Site metric Relative Weighted Site metric
San Jose 50 50%
New York 30 30%
London 20 20%
Total 100 100%
TABLE 6 Example Weighted Site metric configuration
IP address Configured Weighted Site metric Relative Weighted Site metric
San Jose 15 33% (15/45 * 100)
New York 20 44% (20/45 * 100)
London 10 22% (10/45 * 100)
Using the Weighted Site metric, the GSLB algorithm calculates a relative weight for each IP address and selects the IP address with the least relative weight. The GSLB ServerIron ADX uses the following criteria to calculate the relative weight of an IP address:
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The number of times the GSLB ServerIron ADX selected the IP address as the best IP address to reply to a client•
The number of eligible IP addresses to be evaluated by the Weighted Site metric, and the weights of sites to which they belong•
A calculated weight assigned to an IP address, based on the following criteria:•
If the IP address is a real server, then the calculated weight is zero•
If the IP address is a Virtual IP (VIP), the weight is calculated based on the site the VIP belongs to, the weight of the site, and the number of candidate VIPs belonging to the site and being evaluated by the Weighted Site metricIf an IP address has a relative weight of zero, or if an IP address belongs to a site that does not have an assigned weight, the IP address is not selected as the best IP address for a client. Note that all real servers have a relative weight of zero, as do VIPs that belong to sites with no assigned weights. If two or more IP addresses have the same relative weight, or if all of the IP addresses have a relative weight of zero, all of the IP addresses with the same relative weight are passed on to the next step in the GSLB algorithm, where the process of selecting the best IP address continues. Traffic distribution specifications
In general, DNS response selection counters are maintained per IP address, per domain name. For example, suppose you configure three GSLB sites with assigned weights. All three sites host the application www.example1.com and sites New York and London also host ftp.example1com, as illustrated below.
www.example1.com
VIP 10.1.1.1 belongs to San Jose with a weight of 50 VIP 10.1.1.2 belongs to New York with a weight of 30 VIP 10.1.1.3 belongs to London with a weight of 20
ftp.example1.com
VIP 10.1.1.2 belongs to New York with a weight of 30 VIP 10.1.1.3 belongs to London with a weight of 20
Suppose that 10 DNS requests are made to www.example1.com. By viewing the selection counters (using the show gslb dns zone command), you would see that San Jose is selected 5 times (50%), New York is selected 3 times (30%), and London is selected 2 times (20%).
Now suppose that 5 DNS requests are made to ftp.example1.com. In this case, New York receives 3 requests (60%), and London receives 2 requests (40%). This is because counters are maintained per IP address per domain name.
If you consider the total site traffic for both applications, the traffic distribution is as follows: San Jose = 5 (33%); New York = 6 (40%); and London = 4 (26%). The GSLB ServerIron ADX evaluates the results of the weighted metrics with respect to a specific domain name, not an IP address alone.
Configuring Weighted Site metrics
To configure Weighted Site metrics, complete the following tasks. 1. Enable the Weighted Site metric.
3. Configure a weight for the site.
For example, enter commands such as the following.
ServerIronADX(config-gslb-policy)#weighted-site ServerIronADX(config-gslb-policy)#gslb site SanJose ServerIronADX(config-gslb-site-SanJose)#weight 50
Syntax: [no] weighted-site Syntax: gslb site <site name>
The <site name> can have a maximum of 16 characters. Syntax: weight <weight>
The <weight> is a value from 0 to 100. The default value is 0. Displaying results of traffic distribution for Weighted Sites
To view the results of traffic distribution after configuring Weighted Site metrics, enter the following command.
The first example shows the first two sites. Syntax: show gslb traffic site
This command shows the domains hosted by each site. For each domain name, it shows how much traffic was sent to each ServerIron ADX in that site, and the total percentage of traffic sent to the site.
ServerIronADX(config)#show gslb traffic site SITE: local Weight: 50 * a.b.c
DNS Requests: 36
ServerIronADX VIP Selection (%) == === ============= 10.1.1.1 10.1.1.181 9 (25 %) 10.1.1.1 10.1.1.180 9 (25 %) Site Selection for Domain: 18 (50 %)
* b.b.c
DNS Requests: 0
ServerIronADX VIP Selection (%) == === ============= 10.1.1.1 10.1.1.121 0 (0 %) Site Selection for Domain: 0 (0 %)
SITE: TWO Weight: 50 * a.b.c
DNS Requests: 36
ServerIronADX VIP Selection (%) == === ============= 10.1.1.2 10.1.1.182 18 (50 %) Site Selection for Domain: 18 (50 %)
* b.b.c
DNS Requests: 0
ServerIronADX VIP Selection (%) == === ============= 10.1.1.2 10.1.1.122 0 (0 %) Site Selection for Domain: 0 (0 %)
The second example shows the third site.
In the above examples, there are two hosts; a (HTTP) and b (FTP) which belong to the zone b.c. There are three sites as listed below:
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Local (weight: 50; ServerIron ADX: 10.1.1.1; VIPs: 10.1.1.180 (HTTP), 10.1.1.181 (HTTP), 10.1.1.121 (FTP)•
TWO (weight: 50; ServerIron ADX: 10.1.1.2; VIPs: 10.1.1.182 (HTTP), 10.1.1.122 (FTP))•
THREE (weight: 0; ServerIron ADX: 10.1.1.3; VIPs: 10.1.1.183 (HTTP), 10.1.1.123 (FTP)) The IP resolution for the domain names is as follows:•
a.b.c.: 10.1.1.180; 10.1.1.181; 10.1.1.182•
b.b.c.: 10.1.1.121; 10.1.1.122After making 36 requests for domain "a.b.c.", the distribution was: