Failover and Failback between pools using % availability

Hi Kram,

based on the answer i gave you a few weeks ago...

https://devcentral.f5.com/questions/pool-member-failback-condition-48341

... the required iRule would look like that...

when RULE_INIT {
    set static::primary_pool "pool_a"
    set static::primary_failover_value 49
    set static::primary_failback_value 99
    set static::backup_pool "pool_b"
}
when CLIENT_ACCEPTED {
     Check session table if backup mode is currently active
    if { [table lookup "status_$static::primary_pool"] eq "backup" } then {
         Backup mode is currently active. Applying Backup mode availability requirements. Check if primary pool has equal or more than 4 members.
        if { [expr { 100 / [members $static::primary_pool] * [active_members $static::primary_pool] }] >= $static::primary_failback_value] } then {
              Primary pool has equal or more than 4 members. Switching back to primary pool and disable Backup mode.
            table delete "status_$static::primary_pool"
            pool "$static::primary_pool"
        } else {
              Primary pool has less than 4 members. Using backup pool and keeping Backup mode active...
            pool "$static::backup_pool"
        }
    } else {
         Backup mode is currently not active (default). Applying normal availability requirements. Check if primary pool has more than 1 members.
        if { [expr { 100 / [members $static::primary_pool] * [active_members $static::primary_pool] }] > $static::primary_failover_value] } then {
              Primary pool more than 1 member. Using primary pool and keeping Backup mode disabled...
            pool "$static::primary_pool"
        } else {
              Primary pool less than 2 available member. Using the backup pool and enable Backup mode in session table...
            table add "status_$static::primary_pool" "backup" indefinite indefinite 
            pool "$static::backup_pool"
        }
    }
}

Note: The iRule uses a

[expr { 100 / [members $static::primary_pool] * [active_members $static::primary_pool] }]

>=

Note: The additional % value calculation requires additional CPU cycles. Using hardcoded failover/failback values has a much lower CPU overhead.

Cheers, Kai