One very nice feature available on F5 BIGIP appliance is the Priority Group Activation feature. It allows you to organise your pool members into different priority groups which get activated/deactivated automatically, based on the number of pool members online (servicing requests). In simpler terms, it allows you to setup hot-standby pool members.
In this blog I will clarify the following:
- How to configure it?
- How does it actually work?
- Use cases
- Assign pool members to a priority group. The highest the value, the highest the priority; the default priority is 0 (the lowest). Do this for each pool member
- Navigate to LTM :: Pools :: <click on a pool> :: Members :: <click on a member> :: <scroll down to “Priority Group setting” and add a priority group>
- Enable Priority Group Activation; here you specify the minimum number of available servers as a threshold
- Navigate to LTM :: Pools :: <pool> :: Members :: Priority Group Activation <Less than … >
HOW DOES IT WORK
Once enabled, servers get activated in order, based on priority (highest to lowest) once the number of available pool members is lower than the configured threshold.
To explain the algorithm, I came up with the following diagram:
- Capacity Management – say for example you have five servers in a pool; though two of those are log specs and need upgrading. You want to avoid load balancing decisions to those servers unless two of the high spec servers fail.
- Configuration example: Setup the high spec servers in priority group 5; setup low spec servers in priority group 3 (or any other lower than 5). Group activation is set to “Less than 2”
- Error Page in Maintenance Window: you have two servers in a pool and planning to introduce more in the near future. In the meantime, you’d like to use a third, low spec server to host a maintenance page only; this page is displayed in case your production server goes down.
- Configuration example: Setup the production servers in priority group 4; setup the low spec server in priority group 2 (or lower). Set group activation to “Less than 1”.
Rafael A. Couto Cabral • LinkedIn Profile
Cisco | F5 | VMware Certified • PRINCE2 Practitioner
Originally posted 2017-11-17 11:06:34.