How do you implement failover only?

Define priorities on each pool member per the configuration guide. Note that there is an active bug on priorities, check solution to make sure your configuration isn't vulnerable:

 

 

https://tech.f5.com/home/solutions/sol6986.html

Thank You, would this be a "fool proof" solution for failover only? I have set it to 1000:1 ratio, but would be more comfortable if there is an option to specify "backup" node?

Don't confuse ratio with priority. Ratio means that the "backup" server will get every 1001th connection in a two server scenario with your numbers.

Consider this example from page 4-13 of the configuration manual:

pool my_pool {
 lb_mode fastest
 min active members 2
 member 10.12.10.7:80 priority 1
 member 10.12.10.8:80 priority 1
 member 10.12.10.9:80 priority 1
 member 10.12.10.4:80 priority 2
 member 10.12.10.5:80 priority 2
 member 10.12.10.6:80 priority 2
 member 10.12.10.1:80 priority 3
 member 10.12.10.2:80 priority 3
 member 10.12.10.3:80 priority 3
}
Figure 4.1 Sample

The configuration shown in Figure 4.1 has three priority groups, 1, 2, and 3.

Connections are first distributed to all pool members with priority 1 (the

highest priority group). If fewer than two priority 1 members are available,

traffic is directed to the priority 2 members as well. If both the priority 1

group and the priority 2 group have fewer than two members available,

traffic is directed to the priority 3 group. The LTM system continuously

monitors the higher priority groups, and each time a higher priority group

once again has the minimum number of available members, the LTM

system again limits traffic to that group.

Experience and other documents imply that priorities increase as the priority number increases, i.e., members of the priority 1 group would have the lowest priority and those of the priority 3 group the highest, just the opposit of the above description.