Dynamic Load Balancing Methods
--> In the case of dynamic load balancing methods, F5 Load balancer first checks the server performance before making the decision to choose between the pool members.
--> There are following different types of dynamic load balancing methods are available
i) Least Connection
--> F5 LTM creates and maintains connection table to know how many connections are active on each server.
--> In this method before forwarding the client to request to the server, F5 LTM checks connection table and forwards the client request to the server which has least connections on it.
ii) Fastest
--> Distributes new connections to the member or a node that currently has fewest outstanding layer 7 requests.
--> When a connection request is received, the member with fewest connections is chosen.
---> If the associated virtual server does not have both TCP/ Layer 7 Profile then F5 LTM cannot track requests and fastest load balancing will fail and fall back to least connection method.
--> Fastest Load Balancing can be performed based upon node or pool member.
iii) Least Sessions
--> Least session distributes a new connection to the members based on current persistence record associated with the member.
--> Distributes new connections to the member or a node that currently has the fewest number of Persistence records in the Persistence Table.
--> When a connection request is received, the member with fewest persistent connections is chosen.
--> If the Persistence Method is based upon Cookies then load balancing method automatically fallbacks to round-robin load-balancing method.
--> The Load Balancing method cannot be modified based upon the pool member or node similar to least connections or fastest load balancing.
--> The Load Balancing Method is based upon simply the persistence records stored in the Persistence Table.
--> If all the pool members are having the same persistence records in the persistence table then round-robin load balancing will take place.
iv) Ratio Least Sessions
--> It is a combination of Least Sessions and Ratio Load Balancing Methods.
--> The Administrator needs to assign ratios to the Pool Members or Nodes and load balancing is done based upon the ratio and Least Sessions.
--> It is also called as Weighted Least Sessions.
--> In this Example, The next client request will go to Server3 until it matches the ratio configured by the administrator ( 1:2:3) by checking the persistence table.
v) Ratio Least Connections
--> It is a combination of Least Connections and Ratio Load Balancing Methods.
--> The Administrator needs to assign ratios to the Pool Members or Nodes and load balancing is done based upon the ratio and Least Connections.
--> In the case of dynamic load balancing methods, F5 Load balancer first checks the server performance before making the decision to choose between the pool members.
--> There are following different types of dynamic load balancing methods are available
i) Least Connection
--> F5 LTM creates and maintains connection table to know how many connections are active on each server.
--> In this method before forwarding the client to request to the server, F5 LTM checks connection table and forwards the client request to the server which has least connections on it.
--> If multiple servers are having the same amount of connections count then F5 LTM performs round-robin algorithm for the servers which are having the same amount of connections.
--> Least Connection Load balancing can be performed based upon node or pool member.
Note: BIG IP LTM is not going to check the connections the server is having with other servers. It is only going to check the connections the BIG IP LTM is with Pool Member.
--> Distributes new connections to the member or a node that currently has fewest outstanding layer 7 requests.
--> When a connection request is received, the member with fewest connections is chosen.
---> If the associated virtual server does not have both TCP/ Layer 7 Profile then F5 LTM cannot track requests and fastest load balancing will fail and fall back to least connection method.
--> Fastest Load Balancing can be performed based upon node or pool member.
Note: BIG IP LTM is not going to check the connections the server is having with other servers. It is only going to check the connections the BIG IP LTM is with Pool Member.
iii) Least Sessions
--> Least session distributes a new connection to the members based on current persistence record associated with the member.
--> Distributes new connections to the member or a node that currently has the fewest number of Persistence records in the Persistence Table.
--> When a connection request is received, the member with fewest persistent connections is chosen.
--> If the Persistence Method is based upon Cookies then load balancing method automatically fallbacks to round-robin load-balancing method.
--> The Load Balancing method cannot be modified based upon the pool member or node similar to least connections or fastest load balancing.
--> The Load Balancing Method is based upon simply the persistence records stored in the Persistence Table.
--> If all the pool members are having the same persistence records in the persistence table then round-robin load balancing will take place.
iv) Ratio Least Sessions
--> It is a combination of Least Sessions and Ratio Load Balancing Methods.
--> The Administrator needs to assign ratios to the Pool Members or Nodes and load balancing is done based upon the ratio and Least Sessions.
--> It is also called as Weighted Least Sessions.
--> In this Example, The next client request will go to Server3 until it matches the ratio configured by the administrator ( 1:2:3) by checking the persistence table.
v) Ratio Least Connections
--> It is a combination of Least Connections and Ratio Load Balancing Methods.
--> The Administrator needs to assign ratios to the Pool Members or Nodes and load balancing is done based upon the ratio and Least Connections.
--> In this Example, The next client request will go to Server3 until it matches the ratio configured by the administrator ( 1:2:3) by checking the Connection table.
vi) Weighted Least Connection
--> distributes traffic based upon the lowest percentage of each pool member connection capacity.
--> The percentage is decided based upon the current connection count by maximum connection count.
--> In order Weighted Least connection to work we need to configure maximum connection count in pool member or node.
--> Load balancing can be done based upon pool member or node level.
--> For example if a pool member is configured with a connection limit of 10 and it currently handles 2 connections then the percentage is 20%.
--> If there are three pool members with 30%, 40% and 50% in the pool, Any new request will be forwarded to the pool member with 30%.
vii) Observed
--> Distributes the traffic based upon the currently active layer 4 connections to each pool member or node.
--> BIG IP System automatically assigns the ratio to the pool members by looking at the load of the pool members.
--> The pool member with less number of connections will receive the higher ratio and the pool member with more number of connection will receive lower ratio.
--> Load balancing can be done based upon pool member or node level.
--> distributes traffic based upon the lowest percentage of each pool member connection capacity.
--> The percentage is decided based upon the current connection count by maximum connection count.
--> In order Weighted Least connection to work we need to configure maximum connection count in pool member or node.
--> Load balancing can be done based upon pool member or node level.
--> For example if a pool member is configured with a connection limit of 10 and it currently handles 2 connections then the percentage is 20%.
--> If there are three pool members with 30%, 40% and 50% in the pool, Any new request will be forwarded to the pool member with 30%.
vii) Observed
--> Distributes the traffic based upon the currently active layer 4 connections to each pool member or node.
--> BIG IP System automatically assigns the ratio to the pool members by looking at the load of the pool members.
--> The pool member with less number of connections will receive the higher ratio and the pool member with more number of connection will receive lower ratio.
--> Load balancing can be done based upon pool member or node level.
viii) Predictive
--> Similar to Observed load balancing method.
--> It compares the currently active connections on the pool member with the connections it received in the past.
--> This is also known as delta.
--> If the pool member is receiving more connections than in the past then it reduces the ratio value.
--> Load balancing can be done based upon pool member or node level.
IX) Dynamic Ratio
--> Dynamic ratio does load balancing based upon the information gathered from server or pool members.
--> Need to use Performance Monitor for this.
--> In order to gather the information we need to install an agent on the server which communicates with BIG IP System.
--> The agent can be 1) SNMP Agent 2) WMI 3) Realtime Real Server
--> After gathering the information the Performance monitor will assign a weight to each pool member.
--> The pool member with higher weight will receive more connections.
--> Load balancing can be done based upon pool member or node level.
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