Introduction to BIG-IP LTM: Pools

• Create new Pool
  • Configuration – Basic (Figure 1)
  • Configuration – Advanced (Figure 2) 
  • Resources (Figure 3)
  • Load Balancing Method (Figure 4)
  • Priority Group Activation (Figure 5)
• Inside Pool
  • Properties (Figure 6)
  • Members (Figure 7)
    • Member Properties (Figure 8)
    • Health Monitor – Inherit From Pool (Figure 9)
    • Health Monitor – Member Specific (Figure 10)
• Pools Statistics (Figure 11)

Important details about the Pool features

You can configure the BIG-IP system to perform a number of different operations for a pool.

(1) Associating a health monitor with a pool

With the BIG-IP system, you can configure your monitor associations in many useful ways:

• You can associate multiple monitors with the same pool/pool member (Figure 8)
  • You can specify the number of Health Monitor(s) that must be successful before the node is considered up, via “Availability Requirement”
• You can associate a health monitor with an entire pool instead of an individual pool member
  • Pool member health monitors will “inherit from Pool” setting (Figure 9)
• You can associate a health monitor with an individual pool member
  • Pool member health monitors will be “member specific” (Figure 10)

(2) Enable or disable SNAT connections

When configuring a pool, you can specifically disable any SNATs or NATs for any connections that use that pool. By default, these settings are enabled. (Figure 2)

(3) Action when a service becomes unavailable

You can specify the action that you want the BIG-IP system to take when the service on a pool member becomes unavailable.

Possible actions are:

• None. This is the default action.
• The BIG-IP® system sends an RST (TCP-only) or ICMP message.
• the BIG-IP system simply cleans up the connection.
• the BIG-IP system selects a different node.

You should configure the system to select a different node in certain cases only, such as:

• When the relevant virtual server is a Performance (Layer 4) virtual server with address translation disabled.
• When the relevant virtual server’s Protocol setting is set to UDP.
• When the pool is a gateway pool (that is, a pool or routers)

(4) Priority-based member activation

Priority-based member activation is a feature that allows you to categorize pool members into priority groups, so that pool members in higher priority groups accept traffic before pool members in lower priority groups.

The priority-based member activation feature has two configuration settings:

• Priority group activation
  Specify the minimum number of members that must remain available in each priority group in order for traffic to remain confined to that group.
  • The allowed value for this setting ranges from 0 to 65535.
  • Setting this value to 0 disables the feature (equivalent to using the default value of Disabled).
• Priority group
  Specify a priority group for each member when you add that member to the pool.

(5) Slow ramp time

• When you take a pool member offline, and then bring it back online, the pool member can become overloaded with connection requests, depending on the load balancing method for the pool.
• For example, if you use the Least Connections load balancing method, the system sends all new connections to the newly-enabled pool member (because, technically, that member has the least amount of connections).
• With the slow ramp time feature, you can specify the duration of the system sends less traffic to a newly-enabled pool member. The amount of traffic is based on the ratio of how long the pool member is available compared to the slow ramp time, in seconds. Once the pool member is online for a time greater than the slow ramp time, the pool member receives a full proportion of the incoming traffic.

(6) Type of Service (ToS) level

Another pool feature is the ToS level. The ToS level is one means by which network equipment can identify and treat traffic differently based on an identifier in Layer 3 IP Packet.

• As traffic enters the site, the BIG-IP system can set the ToS level on a packet.
  • The BIG-IP system can apply an iRule and send the traffic to different pools of servers based on that ToS level.
  • ToS value is then inspected by upstream devices and given appropriate priority.
• There are 2 options for configuring ToS
  • IP ToS to Client: set ToS within a packet sent to the client.
  • IP ToS to Server: set ToS within a packet sent to the server.
• Available parameter value:
  • Specify: 0-255
  • Pass Through: the system does not change the ToS value within a packet.
  • Mimic: sets the ToS level of outgoing packets to the same ToS value of the most-recently received incoming packet.

(7) Quality of Service (QoS) level

Another setting for a pool is the QoS level. In addition to the ToS level, the QoS level is a means by which network equipment can identify and treat traffic differently based on an identifier in Layer 2 Frame (CoS = Class of Service).

• There are 2 options for configuring CoS
  • Link QoS to Client: set CoS within a packet sent to the client.
  • Link QoS to Server: set CoS within a packet sent to the server.
• Available parameter value:
  • Specify: 0-7
  • Pass Through: the system does not change the CoS value within a packet.

(8) Number of reselect tries

You can specify the number of times that the system tries to contact a new pool member after a passive failure. A passive failure consists of a server-connect failure or a failure to receive a data response within a user-specified interval. The default value of 0 indicates no reselects.

*This setting is for use primarily with TCP profiles. Using this setting with a Fast L4 profile is not recommended.

(9) TCP request queue