Redundant GSS Probing

[rbarroshpcsc]

Hello,

When having two GSSs on two different sites how is it decided if a monitored VIP is up when the GSSs get different results?

Immagine the the GSSM gets a failed probe, but the Standby GSS gets a passed probe.....

Thank you.

[Syed Iftekhar Ahmed]

First of all it should not happen. Although each GSS is probing VIP by itself for both GSSs VIP's status should be either up/down.

If for any reason connectivity between one GSS & VIP is down then GSS will start resolving VIP of a different data center so your application is still up.

GSSs for client requests are selected by the DNS servers authoritative for your domain.Its normally done on roundrobin based (default- but can be changed).

Lets assume we have two datacenters DC1 & DC2 with two vips for the same app VIP1 & VIP2 and similarly two GSSs Gss1 & Gss2.

A request from Client A's DNS server will hit the DNS server authoritative for abc.com. Lets say DNS server selects gss1 for this request if gss1 sees both VIPs up (and lb method on GSS is configured as ordered list , gss1 will always server address of VIP1 unless its down). Client A will hit VIP1 in DC1.

Now lets say another client, client B's DNS server asks (abc.com)'s DNS server for http://www.abc.com , this time DNS server will redirect thid request to gss2. If for some reason for gss2 VIP1 is down then gss2 will ask client B's Dns server to go to VIP2 in DC2.

HTH

Syed Iftekhar Ahmed

[rbarroshpcsc]

Hi Syed,

thanks for you response.

Immagine this scenario:

DC1&DC2

VIP1&VIP2

GSS1&GSS2

both GSS1 and GSS2 are monitoring VIP1. Immagine that a problem occurs in the path between GSS1 and VIP1. The GSS1 to VIP1 probe, fails. However, GSS2 is still able to see VIP1 in a up state.

What is the GSSs behaviour in this case? How will this VIP appear in the Web Gui? UP or DOWN?

Thank You,

[Syed Iftekhar Ahmed]

Each GSS independently polls the answers and in your scenario you will see VIP1 offline for GSS1 and online for GSS2 in the GUI.

Any request hitting GSS1 will not be entertained and request hitting GSS2 will get the VIPs IP from the GSS2.

Syed

[rbarroshpcsc]

What do you mean by requests hiting GSS1 not being entertained? Does it mean that there will be two different answers to the DNS requests: one when the client request hits the GSS1 (which will be the second answer in the ordered list has the probe for the first answer is failing) and another when the client hits the GSS2 (which will be the first answer in the ordered list has its probe is successfull).

[rbarroshpcsc]

Can anyone help?please....;)