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14.1 - Current Release 13.1 13.0 12.1
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Customize your GSLB configuration

September 14, 2021
Contributed by: 
S C

Once your basic GSLB configuration is operational, you can customize it by modifying the bandwidth of a GSLB service, configuring CNAME based GSLB services, static proximity, dynamic RTT, persistent connections, or dynamic weights for services, or changing the GSLB Method.

You can also configure monitoring for GSLB services to determine their states.

These settings depend on your network deployment and the types of clients you expect to connect to your servers.

Modify maximum connections or maximum bandwidth for a GSLB service

You can restrict the number of new clients that can simultaneously connect to a load balancing or content switching virtual server by configuring the maximum number of clients and/or the maximum bandwidth for the GSLB service that represents the virtual server.

To modify the maximum clients or bandwidth of a GSLB service by using the command line interface

At the command prompt, type the following command to modify the maximum number of client connections or the maximum bandwidth of a GSLB service and verify the configuration:

set gslb service <serviceName> [-maxClients <positive_integer>] [-maxBandwidth <positive_integer>]
show gslb service <serviceName>
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Example:

set glsb service Service-GSLB-1 –maxBandwidth 100 –maxClients 100
show gslb service Service-GSLB-1
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To modify the maximum clients or bandwidth of a GSLB service by using the configuration utility

  1. Navigate to Traffic Management > GSLB > Services, and double-click a service.
  2. Click in the Other Settings section and set the following parameters:
    • Max Clients—maxClients
    • Max Bandwidth—maxBandwidth

Create CNAME-based GSLB services

To configure a GSLB service, you can use the IP address of the server or a canonical name of the server. If you want to run multiple services (like an FTP and a Web server, each running on different ports) from a single IP address or run multiple HTTP services on the same port, with different names, on the same physical host, you can use canonical names (CNAMES) for the services.

For example, you can have two entries in DNS as ftp.example.com and www.example.com for FTP services and HTTP services on the same domain, example.com. CNAME-based GSLB services are useful in a multilevel domain resolver configuration or in multilevel domain load balancing. Configuring a CNAME-based GSLB service can also help if the IP address of the physical server is likely to change.

If you configure CNAME-based GSLB services for a GSLB domain, when a query is sent for the GSLB domain, the Citrix ADC appliance provides a CNAME instead of an IP address. If the A record for this CNAME record is not configured, the client must query the CNAME domain for the IP address. If the A record for this CNAME record is configured, the Citrix ADC appliance provides the CNAME with the corresponding A record (IP address). The Citrix ADC appliance handles the final resolution of the DNS query, as determined by the GSLB method. The CNAME records can be maintained on a different Citrix ADC appliance or on a third-party system.

In an IP-address-based GSLB service, the state of a service is determined by the state of the server that it represents. However, a CNAME-based GSLB service has its state set to UP by default; the virtual server IP (VIP) address or metric exchange protocol (MEP) are not used for determining its state. If a desktop-based monitor is bound to a CNAME-based GSLB service, the state of the service is determined according to the result of the monitor probes.

You can bind a CNAME-based GSLB service only to a GSLB virtual server that has the DNS Record Type as CNAME. Also, a Citrix ADC appliance can contain at most one GSLB service with a given CNAME entry.

The following are some of the features supported for a CNAME-based GSLB service:

  • GSLB-policy based site affinity is supported, with the CNAME as the preferred location.
  • Source IP persistence is supported. The persistency entry contains the CNAME information instead of the IP address and port of the selected service.

The following are the limitations of CNAME-based GSLB services:

  • Site persistence is not supported, because the service referenced by a CNAME can be present at any third-party location.
  • Multiple-IP-address response is not supported because one domain cannot have multiple CNAME entries.
  • Source IP Hash and Round Robin are the only load balancing methods supported. The Static Proximity method is not supported because a CNAME is not associated with an IP address and static proximity can be maintained only according to the IP addresses.

Note: The Empty-Down-Response feature should be enabled on the GSLB virtual server to which you bind the CNAME-based GSLB service. If you enable the Empty-Down-Response feature, when a GSLB virtual server is DOWN or disabled, the response to a DNS query, for the domains bound to this virtual server, contains an empty record without any IP addresses, instead of an error code.

To create a CNAME-based GSLB service by using the command line interface

At the command prompt, type:

add gslb service <serviceName> -cnameEntry <string> -siteName <string>
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Example:

add gslb service Service-GSLB-1 -cnameEntry transport.mycompany.com -siteName Site-GSLB-East-Coast
add gslb service Service-GSLB-2 -cnameEntry finance.mycompany.com -siteName Site-GSLB-West-Coast
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To create a CNAME-based GSLB service by using the configuration utility

  1. Navigate to Traffic Management > GSLB > Services.
  2. Create a service, and set the Type to Canonical Name Based.

Configure transition Out-Of-Service State (TROFS) in GSLB

When you configure persistence on a GSLB virtual server to which a service is bound, the service continues to serve requests from the client even after it is disabled, accepting new requests or connections only to honor persistence. After a configured period of time, known as the graceful shutdown period, no new requests or connections are directed to the service, and all of the existing connections are closed.

When disabling a service, you can specify a graceful shutdown period, in seconds, by using the delay argument. During the graceful shutdown period, if the service is bound to a virtual server, its state appears as Out of Service.

Configure dynamic weights for services

In a typical network, there are servers that have a higher capacity for traffic than others. However, with a regular load balancing configuration, the load is evenly distributed across all services even though different services represent servers with different capacities.

To optimize your GSLB resources, you can configure dynamic weights on a GSLB virtual server. The dynamic weights can be based on either the total number of services bound to the virtual server or the sum of the weights of the individual services bound to the virtual server. Traffic distribution is then based on the weights configured for the services.

When dynamic weights are configured on the GSLB virtual server, requests are distributed according to the load balancing method, the weight of the GSLB service, and the dynamic weight. The product of the weight of the GSLB service and the dynamic weight is known as the cumulative weight. Therefore, when dynamic weight is configured on the GSLB virtual server, requests are distributed on the basis of the load balancing method and the cumulative weight.

When dynamic weight for a virtual server is disabled, the numerical value is set to 1. This ensures that the cumulative weight is a non-zero integer at all times.

Dynamic weight can be based on the total number of active services bound to load balancing virtual servers or on the weights assigned to the services.

Consider a configuration with two GSLB sites configured for a domain and each site has two services that can serve the client. If a service at either site goes down, the other server in that site has to handle twice as much traffic as a service at the other site. If dynamic weight is based on the number of active services, the site with both services active has twice the weight of the site with one service down and therefore receives twice as much traffic.

Alternatively, consider a configuration in which the services at the first site represent servers that are twice as powerful as servers at the second site. If dynamic weight is based on the weights assigned to the services, twice as much traffic can be sent to the first site as to the second.

Note: For details on assigning weights to load balancing services, see Assigning Weights to Services.

As an illustration of how dynamic weight is calculated, consider a GSLB virtual server that has a GSLB service bound to it. The GSLB service represents a load balancing virtual server that in turn has two services bound to it. The weight assigned to the GSLB service is 3. The weights assigned to the two services are 1 and 2 respectively. In this example, when dynamic weight is set to:

  • Disabled:The cumulative weight of the GSLB virtual server is the product of the dynamic weight (disabled = 1) and the weight of the GSLB service (3), so the cumulative weight is 3.
  • SERVICECOUNT: The count is the sum of the number of services bound to the load balancing virtual servers corresponding to the GSLB service (2), and the cumulative weight is the product of the dynamic weight (2) and the weight of the GSLB service (3), which is 6.
  • SERVICEWEIGHT: The dynamic weight is the sum of the weights of services bound to the load balancing virtual servers corresponding to the GSLB service (3), and the cumulative weight is the product of the dynamic weight (3) and the weight of the GSLB service (3), which is 9.

Note: Dynamic weights are not applicable when content switching virtual servers are configured.

To configure a GSLB virtual server to use dynamic weights by using the command line interface

At the command prompt, type:

set gslb vserver <name> -dynamicWeight SERVICECOUNT | SERVICEWEIGHT
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Example:

set gslb vserver vserver-GSLB-1 -dynamicWeight SERVICECOUNT
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To set GSLB virtual server to use dynamic weights by using the configuration utility

  1. Navigate to Traffic Management > GSLB > Virtual Servers, double-click the GSLB virtual server whose method you want to change (for example, vserver-GSLB-1).
  2. Click the Method section and, from the Dynamic Weight drop-down list, select SERVICECOUNT or SERVICEWEIGHT.
Customize your GSLB configuration
September 14, 2021
Contributed by: 
S C
September 14, 2021
Contributed by: 
S C

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