Problem this snippet solves:
I share with you one special load balancing scenario that I had to deal with.
Topology:
Requirements:
- There are two pools configured (Pool_A & Pool_B)
- The members of each pool will work using Round Robin LB method.
- One pool will act as active and the other one will be in standby mode.
- Only the pool with active role will be able to process traffic.
- If 2 or more members of Pool_A (initially active) are down, Pool_B (initially standby) asumes the role of active.
- There is no preempt, in case of Pool_B asumes the active role, it will be active until someone decide to roll back to the initial situation (manually).
How to use this snippet:
It's easy to configure. You need to configure a virtual server without default pool and this iRule applied to it.
Considerations:
- The iRule uses a table variable to keep the state of the current active pool.
- The code will use Pool_A as active pool in the first execution.
- You can manually force an active pool disabling the other pool.
- In case you would like to remove this VS indefinitely, you should manually remove the table variable.
Remove Table Variable:
For deleting the table variable you can replace the irule for this one and execute it once.
when CLIENT_ACCEPTED {
table delete -all -subtable "[virtual name]"
log local0. "[virtual name] table was deleted"
}
You can also define a timeout value for the variable instead of using indefinite.
REF - https://devcentral.f5.com/s/articles/v101-the-table-command-advanced-data-expiration
Code :
when CLIENT_ACCEPTED {
# PICK THE LAST POOL SELECTION
set selection [table lookup -subtable "[virtual name]" pool_selection]
# EVAL POOL SELECTION
if { [active_members ] == 0 } {
set selection ""
table replace -subtable "[virtual name]" pool_selection $selection
} elseif { [active_members ] == 0 } {
set selection ""
table replace -subtable "[virtual name]" pool_selection $selection
} elseif { [active_members ] < 3 } {
set selection ""
table replace -subtable "[virtual name]" pool_selection $selection
}
# APPLY POOL SELECTION
switch $selection {
"" {
pool
}
"" {
pool
}
default {
pool
table set -subtable "[virtual name]" pool_selection indefinite indefinite
}
}
} Tested this on version:
12.1