Introduction to GSLB

--> GSLB ( Global Server Load Balancing) is a feature that provides Intelligent DNS Resolution.

--> Intelligent DNS Resolution allows the BIG IP DNS to respond with the best and available IP addresses to the client DNS Query for a given web application.

--> Intelligent DNS Resolution is only recommended if the web application is hosted under multiple data centers so that the traffic can be forwarded intelligently based upon client location.

Physical Components of GSLB:

1) Data Center

--> Location of a group of Physical Servers where the applications are hosted.

--> Only Name is required to create a Data Center object in F5 BIG IP System.

--> If you are having the servers in multiple locations then you have to create multiple Data Centers on BIG IP DNS.

Ex: DataCenter-US, DataCenter-UK

--> Grouping of Servers in the Data Center allows the BIG IP DNS to understand the network topology for the applications.

2) Servers

--> Defines Physical Server which is present on the Data Center.

--> A Server can be one of the below:

i) BIG IP LTM

ii) BIG IP DNS

iii) Standalone Servers/Generic Servers

--> Each and every server can be present in only one data center.

3) Links

--> Physical Internet Connection from Data Center to the Internet.

--> Links are associated with the Servers.

--> If the Data Center contains only one Internet connection then there is no need of creating links on BIG IP DNS.

--> If you are having multiple Internet Connection in each data center then you need to create multiple Links so that it can be useful in Intelligent DNS Resolution.

--> Each and every link configuration contains following parameters:

i) The IP address of the Router from where you are getting the Internet

ii) The name of the Data Center where the Internet Link is connected

iii) Type of monitor you want to use for monitoring the link

Logical Components of GSLB:

1) Wide IP address

--> WIDE IP address is used to provide Intelligent DNS resolution on the BIG IP DNS.

--> WIDE IP address is nothing but Fully Qualified Domain Names ( Ex:www.kareemccie.com)

--> Each and every WIDE IP address is associated with one or multiple pools.

--> Each and every WIDE IP address is associated with the Load Balancing Algorithm.

2) Pools

--> Pools are a logical group of Virtual Servers.

--> Pools can have the virtual servers within a single data center or from different data centers.

--> Each and every Load IP address is associated with the Load Balancing Algorithm.

3) Virtual Server

--> Each and every Virtual Server is represented by IP address and Port Number.

--> Every Server configured under BIG IP DNS contains one or more virtual servers.

--> BIG IP DNS can automatically discover the Virtual servers or can be manually added under the Server Configuration.

--> Automatic Discovery of Virtual Servers is only supported on the Server such as BIG IP LTM.

GSLB

--> Once you create the Wide IP and associate the Pool to it then the BIG IP DNS can perform the Intelligent DNS resolution.

Ex: 

Wide IP: www.kareemccie.com

Pool: Pool_US and Pool_UK

Load Balancing: Topology Load Balancing

--> In the above example, Wide IP address www.kareemccie.com is mapped to multiple pools, and Load Balancing is selected for the Wide IP is Topology Load Balancing.

--> If a client from the US tries to access the website www.kareemccie.com then the BIG IP DNS provides the response with the IP address of US Data Center Virtual Server.

--> If a client from UK tries to access the website www.kareemccie.com then the BIG IP DNS provides the response with the IP address of the UK Data Center Virtual Server.

--> In this way, The BIG IP DNS provides the Intelligent Load Balancing for the distributed applications.

Ref: F5.com