F5 LTM Pools

F5 LTM (Local Traffic Manager) pools are a crucial component for load balancing traffic across multiple servers. Here's a comprehensive summary:A pool is a logical set of servers (nodes/pool members) that receive traffic from a virtual server. When creating a pool, you define the load balancing method to distribute traffic across members.Creating and Viewing LTM NodesNodes represent the physical servers that will be load balanced. To create a node, specify the IP address and service port. You can view existing nodes under "Local Traffic > Nodes" in the GUI or use the "ltm node" TMSH commands.Creating and Viewing LTM PoolsPools contain the nodes that will receive load balanced traffic. Create a pool by adding members (nodes) and configuring properties like load balancing method. View existing pools under "Local Traffic > Pools" or use "ltm pool" TMSH commands.Load Balancing AlgorithmsF5 offers various load balancing methods to distribute traffic across pool members:Round Robin: Cycles through members in orderRatio: Distributes traffic based on pre-defined member weightsDynamic Ratio: Distributes based on various performance metricsLeast Connections: Picks member with fewest active connectionsObserved: Picks members based on faster response timesPredictive: Like Observed, but analyzes performance historyPriority GroupsPriority groups provide failover if all members of a higher priority are unavailable. Configure multiple pools with different priorities to implement primary/backup server groups.Health MonitorsHealth monitors determine if nodes are available to receive traffic based on port, service checks, or external monitors. Associate monitors with pools to dynamically remove failed members.By understanding nodes, pools, load balancing methods, priorities, and monitors, you can effectively configure F5 LTM to optimize application traffic distribution across your server infrastructure.

# (Only needed if you want to name the nodes to be used in the pool, otherwise you can just create a new pool using the IP:Port with no issues)# Create LTM Node to Add to Poolcreate ltm node address # View LTM Nodelist ltm node

# Create Layer 4 TCP Health Check create ltm monitor tcp TCP-80 destination *:80# Create LTM Pool using Least Connections & Layer 4 Health Checkcreate ltm pool load-balancing-mode least-connections-member monitor tcp TCP-80 members add { : : }# Create Layer 7 Health Checkcreate ltm monitor http my_http_monitor recv "HTTP/1.1 200 OK" send "GET /health.php HTTP/1.1\r\nHost: example.com\r\n\r\n"# Create LTM Pool using Least Connections & Layer 7 Health Checkcreate ltm pool load-balancing-mode least-connections-member monitor http my_http_monitor members add { : : }# Modify LTM Pools Health Check Monitor modify ltm pool monitor tcp modify ltm pool monitor http # Add New Pool Members to Existing Poolmodify ltm pool members add { node1: node2: }

View Only Pool Members Status show ltm pool members | grep -E 'member|Member:|Status'View Pool Status & Members Status show ltm pool members show ltm pool members | grep -E 'Avail|State|Reason|Monitor|Member|Pool'View Pool Status show ltm pool To view specific LTM Pool list ltm pool list ltm pool all-propertiesTo view all LTM Pools list ltm pool list ltm pool * all-properties

View Health Monitor list ltm monitor tcp list ltm monitor http View Pool Health Monitor list ltm pool monitor

To disable a pool member's ability to accept new connections while allowing existing connections use "session-disabled"This will prevent the pool member from receiving new traffic, but existing connections will be allowed to timeout gracefullyTo completely disable a pool member & force all existing connections to be dropped you can use "state-down"Disable modify ltm pool members modify { : disabled } modify ltm pool members modify { : state-down } modify ltm pool members modify { : session-disabled }Enable modify ltm pool members modify { : enabled } modify ltm pool members modify { : state-up } modify ltm pool members modify { : session-enabled }Enable/Disable Pool modify ltm pool disabled modify ltm pool enabled

With this setting, if less than 2 members in the highest priority group are available, traffic will go to the next lower priority as well # Enable Priority Groups on Pool modify ltm pool priority-group-activation enabled # Add Pool Members with Priority modify ltm pool members add { 10.2.1.8:80 { priority 10 } 10.2.1.9:80 { priority 5 } } # Modify Existing Pool Members Priority modify ltm pool members modify { 10.2.1.9:80 { priority 3 } } # Set minimum members for Higher Priority - Configure minimum number of members that must remain available in a higher priority group before traffic is also sent to lower priorities modify ltm pool min-active-members <2>

Load Balancing Methodsleast-connections-memberleast-connections-noderound-robinratio-memberdynamic-ratio-memberfastest-app-responseobserved-memberpredictive-memberratio-nodedynamic-ratio-nodefastest-nodeobserved-nodepredictive-node# Modify Pool Load Balancing Mode modify ltm pool load-balancing-mode round-robin - Distributes connections across pool members in a circular and sequential patternratio-member - Distributes connections among pool members based on the ratio weights you definefor each memberdynamic-ratio-member - Distributes connections based on various dynamic ratios, such as thenumber of current connections and CPU utilizationfastest-app-response - Distributes connections to the pool member that is currently respondingthe fastestleast-connections-member - Distributes connections to the pool member that currently has thefewest active connectionsobserved-member - Distributes connections based on which pool member currently exhibits thefastest response times as determined by the BIG-IP systempredictive-member - Distributes connections based on instructions received about systemperformance from a predictive analytics server external to the BIG-IP systemratio-node - Same as ratio-member but based on the server node instead of just the pool memberdynamic-ratio-node - Same as dynamic-ratio-member but based on the server nodefastest-node - Distributes connections to the node that is currently responding the fastestleast-connections-node - Distributes connections to the node that currently has the fewestactive connectionsobserved-node - Same as observed-member but based on the server nodepredictive-node - Same as predictive-member but based on the server node

To create a pool selection iRule on an F5 load balancer, you can use either a data group or a switch-glob statement. Make sure you have the appropriate http profile on the virtual server before implementing. Here's how you can implement both approaches:Example1: This iRule retrieves the requested URI, looks up the corresponding pool name in the "uri_pools" data group, and if found, selects that pool. If no match is found, it selects the "default_pool". # Using a Data Group Pool Selection iRule create data-group type string modify data-group records add { "/account/*" { "pool account_pool" } "/customer/*" { "pool customer_pool" } "/equipment/*" { "pool equipment_pool" } } when HTTP_REQUEST { set uri [HTTP::uri] set pool [class match -value $uri equals -data group/uri_pools] if { $pool != "" } { pool $pool } else { pool default_pool } } # Add the iRule to a Virtual Server modify virtual rules { }Example2: In this example, the iRule uses the switch-glob statement to match the requested URI against different patterns. If the URI starts with "/account/", it selects the "account_pool". If it starts with "/customer/", it selects the "customer_pool", and so on. If no pattern matches, it selects the "default_pool" # Using Switch-Glob Pool Selection iRule when HTTP_REQUEST { switch -glob [HTTP::uri] { "/account/*" { pool account_pool } "/customer/*" { pool customer_pool } "/equipment/*" { pool equipment_pool } default { pool default_pool } } } # Add the iRule to a Virtual Server modify virtual rules { }