BigIP LTM F5 – Balancing Methods

The BigIP F5 LTM supports various load balancing methods. These methods are categorized as either Static or Dynamic. Dynamic load balancing methods are considered balancing methods that take the server performance into consideration.
This article also explains how the BigIP F5 LTM can balance traffic outside of the fore-mentioned Static and Dynamic balancing methods.


Round Robin – Evenly distributes requests to all available pool members.
Ratio – Ratio allows each server to be assigned a ratio value. This is useful for pool members that have greater or lower computing resources then others. Example : Ratio 3:2:1:1. Based upon 8 requests, 3 requests would go to 1, 2 to 2 then 1 to 1.


Least Connections – Traffic is balanced to servers with the least total of current connections.
Fastest – Connections are distributed to pool members based upon server response time.
Observed – This method is the same as ratio but the ratio is assigned by BigIP. Each ratio is calculated based upon the total number of connections currently active on each pool member. A pool member with a lower then average connection count is assigned a ratio of 3. A pool member with a higher than average count is given ratio of 2.
Predictive – Predictive is similar to observed but ratio`s are assigned using much more aggressive ratio values. A pool member with a lower then average connection count is assigned a ratio of 4. A pool member with a higher then average count is given ratio of 1.


Pool Member vs Node

A Node is an IP address, and a Pool Member is an IP:Port combination. Based on this an IP could have serval different applications and be a member of several different pools. This means for load balancing and health monitoring even though a web service (such as tcp/80) may be not be busy, another service such as SQL, could be.  As such, Pool Member based balancing and health monitoring provides a much more effective and logical way in which to distribute traffic.  

Priority group activation

With priority group activation a backup pool of nodes is defined within a server pool. Both the primary and backup pools are assigned priority values  and priority group activation thresholds defined. At the point the pre-configured thresholds are reached the backup pool is activated as the primary pool.

Fallback host (http only)

With fallback host a redirect is configured and sent back to the client in the event of all pool members being offline.

Rick Donato

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