Bug ID 718885: Under certain conditions, monitor probes may not be sent at the configured interval

Last Modified: Jun 20, 2019

Bug Tracker

Affected Product:  See more info
BIG-IP GTM(all modules)

Known Affected Versions:
12.1.0, 12.1.0 HF1, 12.1.0 HF2, 12.1.1, 12.1.1 HF1, 12.1.1 HF2, 12.1.2, 12.1.2 HF1, 12.1.2 HF2, 12.1.3, 12.1.3.1, 12.1.3.2, 12.1.3.3, 12.1.3.4, 12.1.3.5, 12.1.3.6, 13.0.0, 13.0.0 HF1, 13.0.0 HF2, 13.0.0 HF3, 13.0.1, 13.1.0, 13.1.0.1, 13.1.0.2, 13.1.0.3, 13.1.0.4, 13.1.0.5, 13.1.0.6, 13.1.0.7, 13.1.0.8, 13.1.1, 13.1.1.1

Fixed In:
14.1.0, 14.0.0, 13.1.1.2, 12.1.3.7

Opened: May 07, 2018
Severity: 2-Critical
Related AskF5 Article:
K25348242

Symptoms

When sufficient resources are configured with the same monitor interval, and the monitor timeout value is no more than two times the monitor interval, the monitored resource may be marked as unavailable (due to a timeout) then immediately changed to available.

Impact

Monitor probes are not consistently performed at the configured interval.

Conditions

Monitor interval is lower than the number of resources configured with the same monitor interval.

Workaround

Set the monitor interval to a value greater than the number of resources monitored using that same interval value. The key to this workaround is to ensure that the sum of the resources monitored at a given interval is not greater than the interval. That can be accomplished several ways depending on your configuration and requirements. For example, if the monitoring interval is 30 seconds and there are 40 different monitors with a 30-second interval and each monitor is assigned to exactly one resource, there are at least two options: -- Change the interval for 10 of the monitors to a different value. -- Set the monitor interval to 40. Note: If you change the monitor interval, make sure to also change the timeout value to follow best practices: timeout value = (3 x interval) + 1.

Fix Information

Monitoring is now consistently performed at the configured interval regardless of the number of resources with the same monitor interval.

Behavior Change