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Manual Chapter: Configuration Guide for BIG-IP® Local Traffic Management: 4 - Configuring Load Balancing Pools
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4

Configuring Load Balancing Pools


Introducing load balancing pools

In a typical client-server scenario, a client request goes to the destination IP address specified in the header of the request. For sites with a large amount of incoming traffic, the destination server can quickly become overloaded as it tries to service a large number of requests. To solve this problem, the BIG-IP® local traffic management system distributes client requests to multiple servers instead of to the specified destination IP address only. You configure the BIG-IP system to do this when you create a load balancing pool.

What is a load balancing pool?

A load balancing pool is a logical set of devices, such as web servers, that you group together to receive and process traffic. Instead of sending client traffic to the destination IP address specified in the client request, the BIG-IP system sends the request to any of the servers that are members of that pool. This helps to efficiently distribute the load on your server resources.

When you create a pool, you assign pool members to the pool. A pool member is a logical object that represents a physical node (server), on the network. You then associate the pool with a virtual server on the BIG-IP system. Once you have assigned a pool to a virtual server, the BIG-IP system directs traffic coming into the virtual server to a member of that pool. An individual pool member can belong to one or multiple pools, depending on how you want to manage your network traffic.

The specific pool member to which the BIG-IP system chooses to send the request is determined by the load balancing method that you have assigned to that pool. A load balancing method is an algorithm that the BIG-IP system uses to select a pool member for processing a request. For example, the default load balancing method is Round Robin, which causes the BIG-IP system to send each incoming request to the next available member of the pool, thereby distributing requests evenly across the servers in the pool. For a complete list of load balancing methods, see Specifying the load balancing method .

Features of a load balancing pool

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

  • Associate health monitors with pools and pool members
  • Enable or disable SNAT connections
  • Rebind a connection to a different pool member if the originally-targeted pool member becomes unavailable
  • Set the Quality of Service or Type of Service level within a packet
  • Specify a load balancing algorithm for a pool
  • Assign pool members to priority groups within a pool

Creating and modifying load balancing pools

You use the Configuration utility to create a load balancing pool, or to modify a pool and its members. When you create a pool, the BIG-IP system automatically assigns a group of default settings to that pool and its members. You can retain these default settings or modify them. Also, you can modify the settings at a later time, after you have created the pool.

It is helpful to understand that the BIG-IP system designates some settings as basic and others as advanced. If you decide to modify some of the default settings when you create the pool, be sure to select the Advanced option on the screen to view all configurable settings. For more information on basic and advanced settings in general, see Chapter 1, Introducing Local Traffic Management .

Creating and implementing a load balancing pool

Creating and implementing a load balancing pool is a two-task process:

  • First, you must create the pool.
  • Second, you must associate the pool with a virtual server.
Important

When you create a pool, the BIG-IP system places the pool into your current administrative partition. For information on partitions, see the BIG-IP® Network and System Management Guide.

To create a load balancing pool

  1. On the Main tab, expand Local Traffic, and click Pools.
    The Pools screen opens.
  2. In the upper-right corner of the screen, click Create.
    The New Pool screen opens.
  3. Note: If the Create button is unavailable, this indicates that your user role does not grant you permission to create a pool.
  4. From the Configuration list, select Advanced.
  5. For the Name setting, type a name for the pool.
  6. Specify, retain, or change each of the other settings.
    For information on pool settings, see Configuring pool settings , or refer to the online help for this screen.
  7. Click Finished.

To implement a load balancing pool

  1. On the Main tab, expand Local Traffic, and click Virtual Servers.
    The Virtual Servers screen opens.
  2. Click the name of the appropriate virtual server.
    This displays the settings for that virtual server.
  3. On the menu bar, click Resources.
  4. In the Default Pool list, select the name of your newly-created pool.
  5. Click Update.

Modifying a load balancing pool

You can modify any settings configured for an existing pool, including the load balancing method. For information on pool settings, see Configuring pool settings , or see the online help. For information on adding members to an existing pool, see Modifying pool membership .

To modify pool settings

  1. On the Main tab, expand Local Traffic, and click Pools.
    The Pools screen opens.
  2. Click the name of an existing pool.
    This displays the existing settings for that pool.
  3. From the Configuration list, select Advanced.
    This displays the pool settings.
  4. Modify or retain all settings.
  5. Click Update.
  6. If you want to modify the load balancing method or enable or disable priority group activation, locate the menu bar and click Members.
  7. Modify or retain the Load Balancing Method and Priority Group Activation settings.
  8. Click Update.

Modifying pool membership

For an existing load balancing pool, you can either modify existing pool members or add new members to the pool.

Modifying existing pool members

When modifying settings for members of a pool, you can:

  • Enable or disable pool members
  • Remove members from the pool
  • Modify the values of pool member settings

To modify existing pool members

  1. On the Main tab, expand Local Traffic, and click Pools.
    The Pools screen opens.
  2. In the Members column, click the number shown.
    This lists the existing members of the pool.
  3. Locate the Current Members section of the screen.
  4. Modify a pool member:
    1. If you want to enable or disable a pool member, or remove a member from the pool, click the box to the left of a member address. Then click Enable, Disable, or Remove.
    2. If you want to modify the settings for a pool member, click an address and retain or modify pool member settings as needed. For information on pool member settings, see Configuring pool member settings .
  5. Click Update.

Adding members to an existing load balancing pool

Not only can you specify pool members at the time that you create a pool, you can add pool members later. When adding a pool member to an existing pool (as opposed to specifying a pool member during pool creation), you can configure a number of settings for that pool member. The only settings that you must explicitly specify are the Address and Service Port settings. All other settings have default values that you can either retain or adjust, depending on your needs.

Note

If you specify a pool member at the time that you create a pool, you do not see these settings; instead, the BIG-IP system simply assigns default values. However, you can adjust the settings later by modifying the pool member properties. For more information, see Managing pools and pool members .

To add members to a load balancing pool

  1. On the Main tab, expand Local Traffic, and click Pools.
    The Pools screen opens.
  2. In the Members column, click the number shown.
    This lists the existing members of the pool.
  3. In the right side of the screen, click Add.
    The New Pool Members screen opens.
  4. In the Address box, select New Address and type an IP address, or select Node List and select an IP address.
  5. In the Service Port box, type a port number or select a service from the list.
  6. Retain or configure all other settings. For information on pool member settings, see Configuring pool member settings .
  7. Click Finished.

Configuring pool settings

You can configure pool settings to tailor pools to your specific needs. For those settings that have default values, you can retain those default settings or modify them. Also, you can modify any settings either when you create the pool, or at any time after you have created it. For information on how to use the Configuration utility to configure these settings, see Creating and modifying load balancing pools .

Table 4.1 lists the settings that you can configure for a pool, followed by a description of each setting.

Table 4.1 Settings for a load balancing pool
Pool Setting
Description
Default Value
Name
You can specify the user-supplied name of the pool. Specifying a name for a pool is required.
No default value
Health Monitors
You can associate a health or performance monitor with an entire pool, rather than with individual pool members only. This eases the task of configuring health and performance monitoring for multiple web servers.
No default value
Availability Requirement
You can specify the number of monitors that must report a pool member as being available before that member is defined as being in an up state.
All
Allow SNAT
You can configure a pool so that SNATs are automatically enabled or disabled for any connections using that pool.
Yes
Allow NAT
You can configure a pool so that NATs are automatically enabled or disabled for any connections using that pool.
Yes
Action on Service Down
If this setting is enabled and the target pool member goes down, the BIG-IP system tries to choose another pool member and rebind the client connection to a new server connection. Possible values are None, Reject, Drop, and Reselect.
None
Slow Ramp Time
This option causes the BIG-IP system to send a less-than-normal amount of traffic to a newly-enabled pool member for the specified amount of time.
0
IP ToS to Client
You can configure a pool to set a specific Type of Service (ToS) level within a packet sent to a client, based on the targeted pool.
Pass Through
IP ToS to Server
You can configure a pool to set a specific Type of Service (ToS) level within a packet sent to a server, based on the targeted pool.
Pass Through
Link QoS to Client
You can configure a pool to set a specific Quality of Service (QoS) level within a packet sent to a client, based on the targeted pool.
Pass Through
Link QoS to Server
You can configure a pool to set a specific Quality of Service (QoS) level within a packet sent to a server, based on the targeted pool.
Pass Through
Load Balancing Method
You can use the default load balancing method, or you can define another load balancing method, and you can configure priority-based member activation. Different pools can be configured with different load balancing methods.
Round Robin
Priority Group Activation
You can assign pool members to priority groups within the pool.
Disabled
New Members
For each pool that you create, you must specify the servers that are to be members of that pool. Pool members must be specified by their IP addresses. For each pool member, you can also assign a service port, a ratio weight, and a priority group.
No default value

 

Before configuring a pool, it is helpful to have a description of certain pool settings that you might want to change.

Specifying a pool name

The most basic setting you can configure for a pool is the pool name. Pool names are case-sensitive and may contain letters, numbers, and underscores (_) only. Reserved keywords are not allowed.

Each pool that you define must have a unique name.

Associating health monitors with a pool

Monitors are a key feature of the BIG-IP system. Monitors help to ensure that a server is in an up state and able to receive traffic. When you want to associate a monitor with an entire pool of servers, you do not need to explicitly associate that monitor with each individual server. Instead, you can simply use the pool setting Health Monitors to assign the monitor to the pool itself. The BIG-IP system then automatically monitors each member of the pool.

The BIG-IP system contains many different pre-configured monitors that you can associate with pools, depending on the type of traffic you want to monitor. You can also create your own custom monitors and associate them with pools. The only monitor types that are not available for associating with pools are monitors that are specifically designed to monitor nodes and not pools or pool members. These monitor types are:

  • ICMP
  • TCP Echo
  • Real Server
  • SNMP DCA
  • SNMP DCA Base
  • WMI

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

  • You can associate a monitor with an entire pool instead of an individual server. In this case, the BIG-IP system automatically associates that monitor with all pool members, including those that you add later. Similarly, when you remove a member from a pool, the BIG-IP system no longer monitors that server.
  • When a server that is designated as a pool member allows multiple processes to exist on the same IP address and port, you can check the health or status of each process. To do this, you can add the server to multiple pools, and then within each pool, associate a monitor with the that server. The monitor you associate with each server checks the health or performance of the process running on that server.
  • When associating a monitor with an entire pool, you can exclude an individual pool member from being associated with that monitor. In this case, you can associate a different monitor for that particular pool member, or you can exclude that pool member from health monitoring altogether. For example, you can associate pool members A, B, and D with the http monitor, while you associate pool member C with the https monitor.
  • You can associate multiple monitors with the same pool. For instance, you can associate both the http and https monitors with the same pool.

For detailed information on health and performance monitors, see Chapter 12, Configuring Monitors .

Specifying the availability requirements

This setting specifies a minimum number of health monitors. Before the BIG-IP system can report the pool member as being in an up state, this number of monitors, at a minimum, must report a pool member as being available to receive traffic.

To configure this setting, type a number in the Availability Requirement box.

Allowing SNATs and NATs

When configuring a pool, you can specifically disable any secure network address translations (SNATs) or network address translations (NATs) for any connections that use that pool. You do this by configuring the Allow SNAT and Allow NAT settings. By default, these settings are enabled. You can change this setting on an existing pool by displaying the Properties screen for that pool.

One case in which you might want to configure a pool to disable SNAT or NAT connections is when you want the pool to disable SNAT or NAT connections for a specific service. In this case, you could create a separate pool to handle all connections for that service, and then disable the SNAT or NAT for that pool.

For general information on SNATs and NATs, see Chapter 13, Configuring SNATs and NATs .

Specifying action when a service becomes unavailable

The Action on Service Down setting specifies the action that you want the BIG-IP system to take when the service on a pool member becomes unavailable. The possible settings are:

  • None -- The BIG-IP system takes no action. This is the default action.
  • Reject -- The BIG-IP system sends an RST or ICMP message.
  • Drop -- The BIG-IP system simply cleans up the connection.
  • Reselect -- The BIG-IP system selects a different node.

To configure this setting, locate the Action on Service Down setting and select a value from the list.

Configuring a 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 mode for the pool. For example, if you use the Least Connections load balancing mode, the system sends all new connections to the newly-enabled pool member (because technically, that member has the least amount of connections).

When you configure the Slow Ramp Time setting, the system sends less traffic to the newly-enabled pool member. The amount of traffic is based on the ratio of how long the pool member has been available compared to the slow ramp time, in seconds. Once the pool member has been online for a time greater than the slow ramp time, the pool member receives a full proportion of the incoming traffic.

To configure this setting, locate the Slow Ramp Time setting and type a number. This number represents the number of seconds that the system waits before sending traffic to a newly-enabled pool member.

Configuring the Type of Service (ToS) level

Another pool setting for a pool is the Type of Service (ToS) level. The ToS level is one means by which network equipment can identify and treat traffic differently based on an identifier.

As traffic enters the site, the BIG-IP system can set the ToS level on a packet. Using the IP ToS to Server ToS level that you define for the pool to which the packet is sent. the BIG-IP system can apply an iRule and send the traffic to different pools of servers based on that ToS level.

The BIG-IP system can also tag outbound traffic (that is, the return packets based on an HTTP GET) based on the IP ToS to Client ToS value set in the pool. That value is then inspected by upstream devices and given appropriate priority.

For example, to configure a pool so that a ToS level is set for a packet sent to that pool, you can set both the IP ToS to Client level and the IP ToS to Server levels to 16. In this case, the ToS level is set to 16 when sending packets to the client and when sending packets to the server.

Note

If you change the ToS level on a pool for a client or a server, existing connections continue to use the previous setting.

Configuring the Quality of Service (QoS) level

Another setting for a pool is the Quality of Service (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. Essentially, the QoS level specified in a packet enforces a throughput policy for that packet.

As traffic enters the site, the BIG-IP system can set the QoS level on a packet. Using the Link QoS to Server QoS level that you define for the pool to which the packet is sent, the BIG-IP system can apply an iRule that sends the traffic to different pools of servers based on that QoS level.

The BIG-IP system can also tag outbound traffic (that is, the return packets based on an HTTP GET) based on the Link QoS to Client QoS value set in the pool. That value is then inspected by upstream devices and given appropriate priority.

For example, to configure a pool so that a QoS level is set for a packet sent to that pool, you can set the Link QoS to Client level to 3 and the Link QoS to Server level to 4. In this case, the QoS level is set to 3 when sending packets to the client, and set to 4 when sending packets to the server.

Specifying the load balancing method

Load balancing is an integral part of the BIG-IP system. Configuring load balancing on a BIG-IP system means determining your load balancing scenario, that is, which pool member should receive a connection hosted by a particular virtual server. Once you have decided on a load balancing scenario, you can specify the appropriate load balancing method for that scenario.

A load balancing method is an algorithm or formula that the BIG-IP system uses to determine the node to which traffic will be sent. Individual load balancing methods take into account one or more dynamic factors, such as current connection count. Because each application of the BIG-IP system is unique, and node performance depends on a number of different factors, we recommend that you experiment with different load balancing methods, and select the one that offers the best performance in your particular environment.

Using the default load balancing method

The default load balancing method for the BIG-IP system is Round Robin, which simply passes each new connection request to the next server in line. All other load balancing methods take server capacity and/or status into consideration.

If the equipment that you are load balancing is roughly equal in processing speed and memory, Round Robin mode works well in most configurations. If you want to use the Round Robin method, you can skip the remainder of this section, and begin configuring other pool settings that you want to add to the basic pool configuration.

Selecting a load balancing method

Several different load balancing methods are available for you to choose from. If you are working with servers that differ significantly in processing speed and memory, you may want to switch to one of the ratio or dynamic ratio methods.

Note

On certain hardware platforms, additional load-balancing methods might be available.
  • Round Robin
    This is the default load balancing method. Round Robin mode passes each new connection request to the next server in line, eventually distributing connections evenly across the array of machines being load balanced. Round Robin mode works well in most configurations, especially if the equipment that you are load balancing is roughly equal in processing speed and memory.
  • Ratio (member) and Ratio (node)
    The BIG-IP system distributes connections among machines according to ratio weights that you define, where the number of connections that each machine receives over time is proportionate to a ratio weight you define for each machine. These are static load balancing methods, basing distribution on static user-assigned ratio weights that are proportional to the capacity of the servers. Regarding Ratio load balancing:
  • Load balancing calculations may be localized to each pool (member-based calculation) or they may apply to all pools of which a server is a member (node-based calculation). This distinction is especially important with the Ratio method; with the Ratio (member) method, the actual ratio weight is a member setting in the pool definition, whereas with the Ratio (node) method, the ratio weight is a setting of the node.

    The default ratio setting for any node is 1. If you use the Ratio (as opposed to Ratio (member) load balancing method, you must set a ratio other than 1 for at least one node in the configuration. If you do not change at least one ratio setting, the load balancing method has the same effect as the Round Robin load balancing method.

    Warning: If you set the load balancing method to Ratio (node), as opposed to Ratio (Member), you must define a ratio setting for each node.

  • Dynamic Ratio (member) and Dynamic Ratio (node)
    The Dynamic Ratio method is like the Ratio method except that ratio weights are based on continuous monitoring of the servers and are therefore continually changing.
  • This is a dynamic load balancing method, distributing connections based on various aspects of real-time server performance analysis, such as the current number of connections per node or the fastest node response time.

    The Dynamic Ratio method is used specifically for load balancing traffic to RealNetworks® RealSystem® Server platforms, Windows® platforms equipped with Windows Management Instrumentation (WMI), or any server equipped with an SNMP agent such as the UC Davis SNMP agent or Windows 2000 Server SNMP agent. To implement Dynamic Ratio load balancing, you must first install and configure the necessary server software for these systems, and then install the appropriate performance monitor. For more information, see Appendix A, Additional Monitor Considerations .

  • Fastest (node) and Fastest (application)
    The Fastest methods pass a new connection based on the fastest response of all currently active nodes. These methods may be particularly useful in environments where nodes are distributed across different logical networks. Load balancing calculations may be localized to each pool (member-based calculation) or they may apply to all pools of which a server is a member (node-based calculation).
  • Least Connections (member) and Least Connections (node)
    The Least Connections methods are relatively simple in that the BIG-IP system passes a new connection to the node that has the least number of current connections. Least Connections methods work best in environments where the servers or other equipment you are load balancing have similar capabilities.
  • These are dynamic load balancing methods, distributing connections based on various aspects of real-time server performance analysis, such as the current number of connections per node or the fastest node response time.

    Load balancing calculations may be localized to each pool (member-based calculation) or they may apply to all pools of which a server is a member (node-based calculation).

  • Observed (member) and Observed (node)
    The Observed methods use a combination of the logic used in the Least Connections and Fastest modes. With the Observed methods, nodes are ranked based on a combination of the number of current connections and the response time. Nodes that have a better balance of fewest connections and fastest response time receive a greater proportion of the connections. The Observed modes also work well in any environment, but may be particularly useful in environments where node performance varies significantly.
  • These are dynamic load balancing methods, distributing connections based on various aspects of real-time server performance analysis, such as the current number of connections per node or the fastest node response time.

    Load balancing calculations may be localized to each pool (member-based calculation) or they may apply to all pools of which a server is a member (node-based calculation).

  • Predictive (member) and Predictive (node)
    The Predictive methods also use the ranking methods used by the Observed methods, where nodes are rated according to a combination of the number of current connections and the response time. However, with the Predictive methods, the BIG-IP system analyzes the trend of the ranking over time, determining whether a node's performance is currently improving or declining. The nodes with better performance rankings that are currently improving, rather than declining, receive a higher proportion of the connections. The Predictive methods work well in any environment.
  • The Predictive methods are dynamic load balancing methods, distributing connections based on various aspects of real-time server performance analysis, such as the current number of connections per node or the fastest node response time.

    Load balancing calculations may be localized to each pool (member-based calculation) or they may apply to all pools of which a server is a member (node-based calculation).

  • Least Sessions
    The Least Sessions method passes a new connection to the node that has the least number of current sessions. The Least Sessions method work best in environments where the servers or other equipment that you are load balancing have similar capabilities. This is a dynamic load balancing method, distributing connections based on various aspects of real-time server performance analysis, such as the current number of sessions.
  • L3 Address
    The L3 Address method passes connections sequentially to each member, using its IP address. The IP address is a Layer three (L3) address.

Specifying priority-based member activation

You can load balance traffic across all members of a pool or across only members that are currently activated according to their priority number. In priority-based member activation, each member in a pool is assigned a priority number that places it in a priority group designated by that number.

With all pool members available (meaning they are enabled, marked up, and have not exceeded their connection limit), the BIG-IP system distributes connections to all members in the highest priority group only, that is, the group designated by the highest priority number. The Priority Group Activation value determines the minimum number of members that must remain available for traffic to be confined to that group. If the number of available members in the highest priority group drops below the minimum number, the BIG-IP system also distributes traffic to the next higher priority group, and so on. The configuration shown in Figure 4.1 has three priority groups, 3, 2, and 1.

Figure 4.1 Sample pool configuration for priority load balancing
pool my_pool {
lb_mode fastest
min active members 2
member 10.12.10.7:80 priority 3
member 10.12.10.8:80 priority 3
member 10.12.10.9:80 priority 3
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 1
member 10.12.10.2:80 priority 1
member 10.12.10.3:80 priority 1
}

 

Connections are first distributed to all pool members with priority 3 (the highest priority group). If fewer than two priority 3 members are available, traffic is directed to the priority 2 members as well. If both the priority 3 group and the priority 2 group have fewer than two members available, traffic is directed to the priority 1 group. the BIG-IP system continuously monitors the higher priority groups, and each time a higher priority group once again has the minimum number of available members, the BIG-IP system again limits traffic to that group.

Specifying pool members

When you configure this setting, you are specifying the servers (that is, pool members) that will make up the load balancing pool. To specify a pool member, you use the Address and Service Port settings to specify the server's IP address, and a service port.

Optional settings are the ratio weight, applicable when you have selected the load balancing method Ratio (member), Ratio (node), or Dynamic Ratio, and the priority group activation. For more information on these settings, see Configuring pool member settings .

Configuring pool member settings

When adding members to a pool, you can configure a number of settings for that pool member. You configure most of these settings after you have created the load balancing pool. The only settings that you must specify during pool creation are the Address and Service Port settings. All other settings have default values that you can either retain or adjust later, depending on your needs.

For information on adding pool members during pool creation, see Creating and implementing a load balancing pool . For information on adding members to an existing pool, see Adding members to an existing load balancing pool .

Note

By design, a pool and its members always reside in the same partition.

Table 4.2 shows the settings that you can configure for an existing pool member, followed by a description of each setting.

Table 4.2 Configuration settings for an individual pool member
General property
Description
Default Value
Ratio
Specifies the ratio weight that you want to assign to the pool member.
1
Priority Group
Specifies the priority group for the pool member.
1
Connection Limit
Specifies the maximum number of concurrent connections allowed for a pool member.
0
Health Monitors
Specifies whether you want the pool member to inherit the monitor associated with the pool or to use a different monitor.
Inherit From Pool
Select Monitors
Specifies the monitor or monitors that you want to associate with that pool member. This setting is used only when you set the Health Monitors setting to Member Specific.
No default value
Availability Requirement
Specifies a minimum number of health monitors. Before the BIG-IP system can report the pool member as being in an up state, this number of monitors, at a minimum, must report a pool member as being available to receive traffic.
 

 

To adjust settings for a pool member after you have added it to a pool, see To view pool-member properties .

Before adding pool members, it is helpful to have a description of certain pool member settings that you might want to change.

Specifying a ratio weight for a pool member

When using a ratio-based load balancing method for distributing traffic to servers within a pool, you can use the Ratio setting to assign a ratio weight to the server. The ratio weight determines the amount of traffic that the server receives.

The ratio-based load balancing methods are: Ratio (member), Ratio (node), and Dynamic Ratio. For more information on ratio-based load balancing methods, see Specifying the load balancing method , and Appendix A, Additional Monitor Considerations .

Specifying priority-based member activation

The Priority setting assigns a priority number to the pool member. Within the pool, traffic is then load balanced according to the priority number assigned to the pool member. Thus, members that are assigned a high priority receive the traffic until the load reaches a certain level, at which time the traffic goes to members assigned to the next lower priority group.

You use the Priority Group Activation setting to configure the load level that determines when the BIG-IP system begins directing traffic to members of a lower priority. For more information, see Specifying priority-based member activation .

Specifying a connection limit

With the Connection Limit setting, you can specify the maximum number of concurrent connections allowed for a pool member. Note that the default value of 0 (zero) means that there is no limit to the number of concurrent connections that the pool member can receive.

Selecting an explicit monitor association

Once you have associated a monitor with a pool, the BIG-IP system automatically associates that monitor with every pool member, including those members that you add to the pool later. However, in some cases you might want the monitor for a specific pool member to be different from that assigned to the pool. In this case, you must use the Health Monitors setting to specify that you want to explicitly associate a specific monitor with the pool member.

You can also configure this setting to prevent the BIG-IP system from associating any monitor with that pool member.

To explicitly associate a monitor with a pool member, locate the Health Monitors setting and select Member Specific, which causes the Select Monitors setting to appear. Then configure the Select Monitors setting as described in the following section.

To ensure that the BIG-IP system associates no monitor with the pool member, set the Health Monitors setting to None.

Creating an explicit monitor association for a pool member

The BIG-IP system contains many different monitors that you can associate with a pool member, depending on the type of traffic you want to monitor. You can also create your own custom monitors and associate them with pool members. The only monitor types that are not available for associating with pool members are monitors that are specifically designed to monitor nodes and not pools or pool members. These monitor types are:

  • ICMP
  • TCP Echo
  • Real Server
  • SNMP DCA
  • SNMP DCA Base
  • WMI

For detailed information on health and performance monitors, see Chapter 12, Configuring Monitors .

To associate a monitor with an individual pool member, you simply display the pool member settings and set the Health Monitors setting to Member Specific. This displays the Select Monitors setting. Select the monitor that you want to associate with the pool member, and using the left arrows (<<), move the monitor name to the Active box. Clicking Finished or Update activates the monitor association for that pool member only.

Associating multiple monitors with the same pool member

The BIG-IP system allows you to associate more than one monitor with the same server. Using the Configuration utility, you can:

  • Associate more than one monitor with a member of a single pool.
    For example, you can create monitors http1, http2, and http3, where each monitor is configured differently, and associate all three monitors with the same pool member. In this case, the pool member is marked as down if any of the checks are unsuccessful.
  • Assign one IP address and service to be a member of multiple pools.
    Then, within each pool, you can associate a different monitor with that pool member. For example, suppose you assign the server 10.10.10:80 to three separate pools: my_pool1, my_pool2, and my_pool3. You can then associate all three custom HTTP monitors to that same server (one monitor per pool). The result is that the BIG-IP system uses the http1 monitor to check the health of server 10.10.10.:80 in pool my_pool1, the http2 monitor to check the health of server 10.10.10.:80 in pool my_pool2, and the http3 monitor to check the health of server 10.10.10:80 in pool my_pool3.

You can make multiple-monitor associations either at the time you add the pool member to each pool, or by later modifying a pool member's properties.

Specifying an availability requirement

The Availability Requirement setting specifies a minimum number of health monitors. Before the BIG-IP system can report the pool member as being in an up state, this number of monitors, at a minimum, must report a pool member as being available to receive traffic.

Managing pools and pool members

When generally managing pools and pool members, you typically need to view existing pool or pool member configurations. Occasionally, you might need to perform other management tasks as well. Using the Configuration utility, you can:

  • Manage pools
  • Manage pool members
  • Disable monitor associations for pools and pool members
  • View statistics for pools and pool members

An important part of managing pools and pool members is viewing and understanding the status of a pool or pool member at any given time. The Configuration utility indicates status by displaying one of several icons, distinguished by shape and color, for each pool or pool member:

  • The shape of the icon indicates the status that the monitor has reported for that pool or pool member. For example, a circle-shaped icon indicates that the monitor has reported the pool member as being up, whereas a diamond-shaped icon indicates that the monitor has reported the pool member as being down.
  • The color of the icon indicates the actual status of the node itself. For example, a green shape indicates that the node is up, whereas a red shape indicates that the node is down. A black shape indicates that user-intervention is required.

To further understand these status icons, see Understanding pool status and Understanding pool-member status .

For information on modifying pool properties, see Modifying a load balancing pool . For information on modifying pool-member properties, see Modifying existing pool members .

Managing pools

There are certain pool-specific tasks that you can perform on the BIG-IP system to maintain existing load-balancing pools. For those pools that you have permission to manage, you can view a list of pools, display the properties of a pool, view the status of a pool, or delete a pool.

Note

You can manage only those pools that you have permission to manage, based on your user role and partition access assignment.

Viewing a list of pools

You can view a list of the existing pools that you have permission to view. When you display the list of pools, the Configuration utility displays the following information about each pool:

  • Status
  • Name
  • Partition in which the pool resides
  • Number of pool members

Use the following procedure to view a list of pools defined on the BIG-IP system.

To view the list of pools

On the Main tab, expand Local Traffic, and click Pools.
This opens the Pools screen and displays a list of the pools that you have permission to view.

Viewing pool properties

You can use the Configuration utility to view the general properties of a pool. Note that you can only view properties of those pools that you have permission to view. The pool properties and their descriptions are:

  • Name
    The unique name that you assigned to the pool. An example of a pool name is my_http_pool.
  • Partition
    The administrative partition in which the pool resides. For more information on administrative partitions, see the BIG-IP® Network and System Management Guide.
  • Availability
    The status of the pool, based on:
    • Whether the pool is enabled
    • The status of parent nodes
    • The status of pool members based on reports from associated health monitors

To view pool properties

  1. On the Main tab, expand Local Traffic, and click Pools.
    The Pools screen opens.
  2. Click a pool name.
    This displays the properties for that pool.

Understanding pool status

At any time, you can determine the status of a pool. The status of a pool is based solely on the status of its members. Using the Configuration utility, you can find this information by viewing the Availability property of the pool. You can also find this information by displaying the list of pools and checking the Status column.

The Configuration utility indicates pool status by displaying one of several icons, distinguished by shape and color. To understand these icons, see Table 4.3 . To locate the icons within the Configuration utility, see To view pool properties . For background information on status icons, see Managing pools and pool members

Table 4.3 Explanation of status indicators for pools
Status indicator
Explanation
At least one pool member is available for processing traffic.

 

 

No pool members are currently available but any one of them could become available later, with no user action required. An example of an unavailable pool member becoming available automatically is when the number of concurrent connections to the pool member no longer exceeds the value defined in the pool member's Connection Limit setting.

 

 

All pool members are unavailable and therefore cannot accept traffic. A reason for a pool member being unavailable is that an associated EAV monitor has detected that the pool member is unavailable. When pool status is red, user action is usually required.

 

 

The status of at least one pool member is unknown, and no other pool members are available. Sample reasons for unknown pool-member status are:
One or more pool members has no associated monitor.
Monitor results are not available yet.
The pool member's IP address is misconfigured.
The parent node has been disconnected from the network.

.

Deleting a pool

To delete an existing pool, use the following procedure. For information on removing individual pool members from a pool, see Modifying existing pool members .

Before deleting a pool, you must first remove the pool as a resource from the virtual server.

To delete a pool

  1. On the Main tab, expand Local Traffic, and click Pools.
    The Pools screen opens.
  2. In the left column next to a pool name, check the Select box.
  3. Click Delete.
    This displays the Delete Confirmation screen.
  4. Click Delete.

Managing pool members

There are certain tasks specific to pool members that you can perform on the BIG-IP system to maintain those existing pool members. For those pool members that you have permission to manage, you can view a list of pool members, display the properties of the pool member, view the status of a pool member, enable or disable a pool member, or delete a pool member.

Note

You can manage only those pool members that you have permission to manage, based on your user role and partition access assignment.

Viewing a list of pool members

You can view a list of the pool members that you have permission to view. When you display the list of pool members, the Configuration utility displays the following information about each member:

  • Status
  • IP address and service
  • Ratio
  • Priority group

Use the following procedure to view a list of pool members defined for a pool.

To view a list of pool members

  1. On the Main tab, expand Local Traffic, and click Pools.
    The Pools screen opens.
  2. In the Name column, click the name of the relevant pool.
  3. On the menu bar, click Members.
    This lists the members of the pool.

Viewing pool-member properties

You can use the Configuration utility to view the general properties of an individual pool member. These properties and their descriptions are:

  • Address
    The IP address of the associated node.
  • Service port
    The port number of the relevant service.
  • Partition
    The partition in which the pool member resides. This partition always matches the partition of the pool itself.
  • Parent node
    The node (IP address) with which the pool member is associated. For example, if the pool member is 10.10.10.22:80, then the parent node is 10.10.10.22.
  • Availability
    The status of the pool member, based on the parent node, the pool, and the monitor with which the pool member is associated.
  • Health monitors
    The health monitors that are associated with the pool member.
  • Current connections
    The number of current connections that the pool member has received.
  • State
    The state of the traffic that you want the pool member to receive. Possible states are:
    • Enabled (All Traffic Allowed)
    • Disabled (Only persistent or active connections allowed)
    • Forced offline (Only active connections allowed)

To view pool-member properties

  1. On the Main tab, expand Local Traffic, and click Pools.
    The Pools screen opens.
  2. In the Name column, click the name of the relevant pool.
  3. On the menu bar, click Members.
    This lists the members of the pool.
  4. In the Current Members column, click a pool member IP address and port number.
    This displays the properties for that pool member.

Understanding pool-member status

At any time, you can determine the status of a pool member. Using the Configuration utility, you can find this information by viewing the Availability property of the pool member. You can also find this information by displaying the list of pool members and viewing the Status column.

The Configuration utility indicates pool member status by displaying one of several icons, distinguished by shape and color. To further understand these status icons, see Table 4.4 . To view the icons within the Configuration utility, see To view pool-member properties . For background information on status icons, see Managing pools and pool members .

Tip


You can manually set the availability of a pool member by configuring the Manual Resume attribute of the associated health monitor. For more information, see Setting the Manual Resume attribute, in Chapter 12.

 

Table 4.4 Explanation of status icons for pool members
Status indicator
Explanation
State property is set to...
The pool member is set to Enabled, the parent node is up, and a monitor has marked the pool member as up.
Enabled (All Traffic Allowed)

 

 

The pool member is unavailable, but could become available later with no user interaction required. This status occurs when the number of concurrent connections has exceeded the limit defined in the pool member's Connection Limit setting.
Enabled (All Traffic Allowed)

 

 

The pool member is unavailable because either the parent node is down, a monitor has marked the pool member as down, or a user has disabled the pool member.
Enabled (All Traffic Allowed)

 

 

The pool member is set to Disabled, although a monitor has marked the pool member as up. To resume normal operation, you must manually enable the pool member.
Disabled (Only persistent or active connections allowed)

 

 

The pool member is set to Disabled and is offline because the parent node is down. To resume normal operation, you must manually enable the pool member.
Forced Offline (Only active connections allowed)

 

 

The pool member is set to Disabled and is offline because a user disabled it. To resume normal operation, you must manually enable the pool member.
Disabled (Only persistent or active connections allowed)

 

 

The pool member is set to Disabled and is offline because either the parent node is down, or a monitor has marked the pool member as down. To resume normal operation, you must manually enable the pool member.
Forced Offline (Only active connections allowed)

 

 

The pool member or node has no monitor associated with it, or no monitor results are available yet
Enabled (All Traffic Allowed)

 

Note

Black status icons indicate that the Manual Resume attribute is enabled on the associated monitor. For more information, see Chapter 12, Configuring Monitors .

Enabling or disabling a pool member

You can use the Configuration utility to enable or disable individual pool members. When you enable or disable a pool member, you indirectly set the value of the pool member's State property, in the following way:

  • Enable
    Sets the State property of the pool member to Enabled (All traffic allowed).
  • Disable
    Sets the State property of the pool member to Disabled (Allow persistent and active connections only).

Note that the difference between a disabled pool member and a pool member that a monitor reports as down is that a disabled pool member continues to process persistent and active connections. Conversely, a pool member reported as down processes no connections whatsoever.

The status icons on the pool-member list screen and properties screen indicate whether a pool member is currently enabled or disabled. For more information on pool member status, see Understanding pool-member status .

To enable or disable a pool member

  1. On the Main tab, expand Local Traffic, and click Pools.
    This displays the list of pools that you have permission to view.
  2. Locate the IP address and port number of the pool member you want to enable or disable.
  3. In the column to the left, check the Select box.
  4. At the bottom of the screen, click Enable or Disable.

Deleting a pool member

To delete an existing pool, use the following procedure. For information on removing individual pool members from a pool, see Modifying existing pool members .

Before deleting a pool, you must first remove the pool as a resource from the virtual server.

To delete a pool member

  1. On the Main tab, expand Local Traffic, and click Pools.
    The Pools screen opens.
  2. In the Name column, click a pool name.
    This displays the properties of the pool.
  3. On the menu bar, click Members.
    This displays the list of pool members.
  4. In the left column next to a pool member address, check the Select box.
  5. Click Delete.
    This displays the Delete Confirmation screen.
  6. Click Delete.

Removing monitor associations

You can remove any existing monitor associations for a pool or pool member.

To remove a monitor from a pool, access the properties page for the pool and change the Health Monitors setting by moving the monitor name in the Active box to the Available box.

To remove an explicit monitor association on an individual pool member, access the properties page for the pool member and change the Health Monitors setting to either Inherit from Pool or None. Selecting None excludes the pool member from any monitoring that you have configured on that pool.

Viewing pool and pool member statistics

Using the Configuration utility, you can view statistics related to existing pools and pool members.

To view pool and pool member statistics, display the list of existing pools or the list of existing pool members. Then click Statistics on the menu bar. This opens the Statistics screen, which shows statistics for all existing pools and their pool members.

The types of statistics shown are:

  • Bits (in and out)
  • Packets (in and out)
  • Connections (current, maximum, and total)



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