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How often does BIG-IP resolve fqdn nodes?

rob_carr
MVP
MVP

We have a configuration where we need to forward client requests to cloud-based hosts, and it generally works well, but we are looking into some occasional outages that appear to be happening. In the course of our investigation I was asked how often the BIG-IP will resolve FQDNs to add or delete ephemeral nodes. I suspect the BIG-IP is using the Interval value specified when creating a FQDN node, but the description is a bit cryptic in my opinion

 

In the LTM Implementations manual chapter Configuring the BIG-IP System to Auto-Populate Pools, the process of defining a node via FQDN is described. In this description, the Interval parameter is defined as below:

 

"In the Interval field, type the number of seconds before the system creates new ephemeral nodes or deletes expired ephemeral nodes based on the IP addresses returned in response to a DNS query for the FQDN of the node. The default is the TTL of the IP address in the DNS response."

 

The description mentions create or delete, but not resolve. Is resolve implied and the Interval value is in fact how often the resolution is completed?

4 REPLIES 4

According to GUI's help it's implied (3600 seconds or 1 hour):

 

"Specifies the interval in which a query occurs, when the DNS server is up. The associated monitor attempts to probe three times, and marks the server down if it there is no response within the span of three times the interval value, in seconds. The default is 3600."

 

Hope that's what you're looking for.

Hey Rodrigo,

 

Thanks for that. It hadn't occurred to me that the help documentation in the GUI would change between the creating a node screen and the viewing a created node screen, but it does. The Interval and Down Interval help information isn't present when you open the help tab on an existing node.

 

It's also worth noting that the description in the help documentation available via GUI is completely different from what is present in the Implementation manual:

 

From the help documentation available in the GUI:

Interval

Specifies the interval in which a query occurs, when the DNS server is up. The associated monitor attempts to probe three times, and marks the server down if it there is no response within the span of three times the interval value, in seconds. The default is 3600.

Down Interval

Specifies the interval in which a query occurs, when the DNS server is down. The associated monitor continues polling as long as the DNS server is down. The default is 5.

 

From the LTM Implementation manual (consistent across v13/14/15):

 

In the Interval field, type the number of seconds before the system creates new ephemeral nodes or deletes expired ephemeral nodes based on the IP addresses returned in response to a DNS query for the FQDN of the node. The default is the TTL of the IP address in the DNS response.

 

In the Down Interval field, type the number of seconds the system waits to mark an FQDN node down following a DNS query failure.

 

 

Yes, you're correct. However, FYI I found written confirmation from Product Development internally that the info I gave you is the correct one. Cheers.

Thanks for the extra effort.