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Manual Chapter: Nodes
Manual Chapter
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About nodes

A node is a logical object on the BIG-IP Local Traffic Manager system that identifies the IP address of a physical resource on the network. You can explicitly create a node, or you can instruct Local Traffic Manager (LTM) to automatically create one when you add a pool member to a load balancing pool.

The difference between a node and a pool member is that a node is designated by the device’s IP address only (10.10.10.10), while designation of a pool member includes an IP address and a service (such as 10.10.10:8).

A primary feature of nodes is their association with health monitors. Like pool members, nodes can be associated with health monitors as a way to determine server status. However, a health monitor for a pool member reports the status of a service running on the device, whereas a health monitor associated with a node reports status of the device itself.

Nodes are the basis for creating a load balancing pool. For any server that you want to be part of a load balancing pool, you must first create a node, that is, designate that server as a node. After designating the server as node, you can add the node to a pool as a pool member. You can also associate a health monitor with the node, to report the status of that server.

About the node address setting

This setting specifies the IP address of the node. If you are using a route domain other than route domain 0, you can append a route domain ID to this node address. For example, if the node address applies to route domain 1, then you can specify a node address of 10.10.10.10.:%1.

About health monitor association

Using Local Traffic Manager, you can monitor the health or performance of your nodes by associating monitors with those nodes. This is similar to associating a monitor with a load balancing pool, except that in the case of nodes, you are monitoring the IP address, whereas with pools, you are monitoring the services that are active on the pool members.

Local Traffic Manager (LTM) contains many different pre-configured monitors that you can associate with nodes, depending on the type of traffic you want to monitor. You can also create your own custom monitors and associate them with nodes. The only pre-configured monitors that are not available for associating with nodes are monitors that are specifically designed to monitor pools or pool members rather than nodes.

Note: Any monitor that you associate with a node must reside either in partition Common or in the partition that contains the node.

There are two ways that you can associate a monitor with a node: by assigning the same monitor (that is, a default monitor) to multiple nodes at the same time, or by explicitly associating a monitor with each node as you create it.

About monitors and automatic node creation

If you create a pool member without first creating the parent node, Local Traffic Manager automatically creates the parent node for you. Fortunately, you can configure Local Traffic Manager (LTM) to automatically associate one or more monitor types with every node that LTM creates. This eliminates the task of having to explicitly choose monitors for each node.

Keep the following in mind when working with default monitors:

  • If a user with permission to manage objects in partition Common disables a monitor that is designated as the default monitor for nodes (such as the icmp monitor), this affects all nodes on the system. Ensure that the default monitor for nodes always resides in partition Common.
  • To specify default monitors, you must have the Administrator user role assigned to your user account.
  • If all nodes reside in the same partition, the default monitor must reside in that partition or in partition Common. If nodes reside in separate partitions, then the default monitor must reside in partition Common.

About monitors and explicit node creation

Sometimes, you might want to explicitly create a node, rather than having Local Traffic Manager create the node automatically. In this case, when you create the node, you can either associate non-default monitors with the node, or associate the default monitors with the node.

About monitor removal

You can remove a monitor that is explicitly associated with a specific node. When removing a monitor associated with a specific node, you can either remove the monitor association altogether, or change it so that only the default monitor is associated with the node.

Alternatively, you can remove any default monitors, that is, monitors that Local Traffic Manager automatically associates with any node that you create.

About node availability

You can specify the minimum number of health monitors that must report a node as being available to receive traffic before Local Traffic Manager reports that node as being in an up state.

About the ratio weight setting

When you are using the Ratio load balancing method, you can assign a ratio weight to each node in a pool. LTM uses this ratio weight to determine the correct node for load balancing.

Note that at least one node in the pool must have a ratio value greater than 1. Otherwise, the effect equals that of the Round Robin load balancing method.

About the connection rate limit setting

The connection rate limit setting specifies the maximum rate of new connections allowed for the node. When you specify a connection rate limit, the system controls the number of allowed new connections per second, thus providing a manageable increase in connections without compromising availability. The default value of 0 specifies that there is no limit on the number of connections allowed per second.

About node state

A node must be enabled in order to accept traffic. When a node is disabled, Local Traffic Manager allows existing connections to time out or end normally. In this case, the node can accept new connections only if the connections belong to an existing persistence session. (In this way, a disabled node differs from a node that is set to down. The down node allows existing connections to time out, but accepts no new connections whatsoever.)

About node status

At any time, you can determine the status of a node, using the Configuration utility. You can find this information by displaying the list of nodes and viewing the Status column, or by viewing the Availability property of a node.

The Configuration utility indicates status by displaying one of several icons, distinguished by shape and color:

  • The shape of the icon indicates the status that the monitor has reported for that node.
  • The color of the icon indicates the actual status of the node.
Tip: You can manually set the availability of a node with the Manual Resume attribute of the associated health monitor.
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