Product Documentation
ADC
14.1 - Current Release 13.1 13.0 12.1
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GSLB algorithms

October 14, 2022
Contributed by: 
C S

The following algorithms are supported for GSLB.

  • Round Robin: When a GSLB virtual server is configured to use the round robin method, it continuously rotates a list of the services that are bound to it. When the virtual server receives a request, it assigns the connection to the first service in the list, and then moves that service to the bottom of the list.

  • Least Response Time: When the GSLB virtual server is configured to use the least response time method, it selects the service with the lowest value. Where, lowest value = current active connections X average response time.

    You can configure this method for HTTP and Secure Sockets Layer (SSL) services only. The response time (also called Time to First Byte, or TTFB) is the time interval between sending a request packet to a service and receiving the first response packet from the service. The NetScaler appliance uses response code 200 to calculate TTFB.

  • Least Connections: When a GSLB virtual server is configured to use the least connection GSLB algorithm (or method), it selects the service with the fewest active connections. This is the default method, because, in most circumstances, it provides the best performance.
  • Least Bandwidth: A GSLB virtual server configured to use the least bandwidth method selects the service that is currently serving the least amount of traffic, measured in megabits per second (Mbps).
  • Least Packets: A GSLB virtual server configured to use the least packets method selects the service that has received the fewest packets in the last 14 seconds.
  • Source IP Hash: A GSLB virtual server configured to use the source IP hash method uses the hashed value of the client IPv4 or IPv6 address to select a service. To direct all requests from source IP addresses that belong to a particular network to a specific destination server, you must mask the source IP address. For IPv4 addresses, use the netMask parameter. For IPv6 addresses, use the v6NetMaskLength parameter.
  • Custom Load: Custom load balancing is performed on server parameters such as CPU usage, memory, and response time. When using the custom load method, the Citrix ADC appliance usually selects a service that is not handling any active transactions. If all of the services in the GSLB setup are handling active transactions, the appliance selects the service with the smallest load. A special type of monitor, known as a load monitor, calculates the load on each service in the network. The load monitors do not mark the state of a service, but they do take services out of the GSLB decision when those services are not UP.
  • Static Proximity: GSLB uses an IP-address based static proximity database to determine the proximity between the client’s local DNS server and the GSLB sites. The Citrix ADC appliance responds with the IP address of a site that best matches the proximity criteria.
  • Round Trip Time: RTT is a measure of time or delay in the network between the client’s local DNS server and a data resource. The Citrix ADC appliance probes the client’s local DNS server and gathers RTT metric information. The appliance then uses this metric to make its load balancing decision. Global server load balancing monitors the real-time status of the network and dynamically directs the client request to the data center with the lowest RTT value.
  • API Method: GSLB uses a REST API to determine the best performing GSLB service. In the API method, when GSLB receives a DNS request from a client, it evaluates the request against the specified rule.

For more details, see Load Balancing.

GSLB algorithms
October 14, 2022
Contributed by: 
C S
October 14, 2022
Contributed by: 
C S

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