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Manual Chapter: Configuration Guide for BIG-IP® Global Traffic Management: 8 - Managing Connections
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8

Managing Connections


Introducing connection management

When you integrate a Global Traffic Manager into your network, one of its primary responsibilities is to load balance incoming connection requests to the virtual server resource that best fits the configuration parameters you defined. However, load balancing is only one part of managing connections to your network resources. Additional issues that you must consider include:

  • Resource health
    Resource health refers to the ability of a given resource to handle incoming connection requests. For example, the Configuration utility uses a green circle to identify a resource, such as a wide IP, that has available pools and virtual servers, while a pool that is down appears as a red diamond. These visual clues can help you identify connection issues quickly and efficiently.
  • Resource availability
    Resource availability refers to the settings within the Configuration utility that you use to control when a resource is available for connection request. For example, you can establish limit settings, which instruct the Global Traffic Manager to consider a resource as unavailable when a statistical threshold (such as CPU usage) is reached.
  • Restoring availability
    When a resource goes offline, the Global Traffic Manager immediately sends incoming connection requests to the next applicable resource. When you bring that resource online again, you can control how to restore its availability to the Global Traffic Manager, ensuring that connections are sent to the resource only when it is fully ready to receive them.
  • Persisting connections
    Certain interactions with your network require that a given user access the same virtual server resource until their connection is completed. An example of this situation is an online store, in which you want the user to access the same virtual server for their shopping cart until they place their order. With the Global Traffic Manager, you can configure your load balancing operations to take persistent connections into account.
  • Selecting a last resort pool
    The Global Traffic Manager includes the ability to create a last resort pool. A last resort pool is a collection of virtual servers that are not used during normal load balancing operations. Instead, these virtual servers are held in reserve unless all other pools for a given wide IP become unavailable.

In addition, it is important to understand what happens when the Global Traffic Manager cannot find an available resource with which to respond to a connection request. You can find more information on this topic in Determining resource health , following.

Determining resource health

In the Global Traffic Manager, resource health refers to the ability of a given resource to handle incoming connection requests. The Global Traffic Manager determines this health through the use of limit settings, monitors, and dependencies on other network resources.

The health of a resource is indicated by a status code in the Configuration utility. A status code is a visual representation of the availability of a given resource. The Global Traffic Manager displays these status codes in the main screens for a given resource. The types of status codes available for a resource are:

  • Blue
    A blue status code indicates that the resource has not been checked. This status often appears when you first add a resource into the Configuration utility.
  • Green
    A green status code indicates that the resource is available and operational. The Global Traffic Manager uses this resource to manage traffic as appropriate.
  • Red
    A red status code indicates that the resource did not respond as expected to a monitor. The Global Traffic Manager uses this resource only when two conditions are met:
    • The Global Traffic Manager is using the load balancing mode specified in the Fallback load balancing setting.
    • The Fallback load balancing setting for the pool is not None.
  • Yellow
    A yellow status code indicates that the resource is operational, but has exceeded one of its established bandwidth thresholds. The Global Traffic Manager uses a resource that has a yellow status code only if no other resource is available.
  • Black
    A black status code indicates that the resource has been manually disabled and is no longer available for load balancing operations.

As the preceding list illustrates, the health of a resource does not necessarily impact the availability of that resource. For example, a virtual server that has a red status code could still be selected by the Global Traffic Manager.

To view the resource health of a given resource

  1. On the Main tab of the navigation pane, expand Global Traffic Manager.
  2. Click the resource type that you want to view, such as Wide IPs.
    The main screen for the resource opens. This screen displays a list of the resources of that type currently managed through the Global Traffic Manager, including the latest status code for each resource.

Determining resource availability

To load balance effectively, the Global Traffic Manager must determine whether the appropriate resources are available. In the context of the Global Traffic Manager, availability means that the resource meets one or more sets of pre-defined requirements. These requirements can be a set of statistical thresholds, a dependency on another resource, or set of values returned by a monitoring agent. If a resource fails to meet one or more of these requirements, the Global Traffic Manager considers it unavailable and attempts to select the next resource based on the load balancing methodology you defined.

The Global Traffic Manager includes three methods of determining resource availability:

  • Limit settings
  • Monitor availability requirements
  • Virtual server dependencies

The following sections describe each of these methods and how you can configure them within the Global Traffic Manager.

Establishing limit settings

One of the methods for determining the availability of a resource is to establish limit settings. A limit setting is a threshold for a particular statistic associated with a system.

The Global Traffic Manager supports the following limit settings:

  • Kilobytes
  • Packets
  • Total Connections

For BIG-IP systems, the Global Traffic Manager also supports a Connections limit setting.

For hosts, the Global Traffic Manager also supports CPU and Memory limit settings.

To establish limit settings for a BIG-IP system

  1. On the Main tab of the navigation pane, expand Global Traffic and then click Servers.
    The main screen for servers opens.
  2. Click the name of the server that you want to configure.
    The properties screen for the server appears.
  3. From the Configuration list, select Advanced.
    This displays additional fields, and allows you to modify additional default settings.
  4. For each limit setting you want to configure, select Enabled from the corresponding list.
    The screen refreshes to show a box in which you can type a value for the limit setting.
  5. Type the value for each limit setting in the corresponding box.
  6. Click the Update button to save your changes.

Using monitors to determine availability

Another method for determining the availability of a given resource is through the use of monitors. A monitor is a software utility that specializes in a specific metric of a Global Traffic Manager resource. You can customize monitors to be as specific or as general as needed.

To illustrate the use of monitors to determine the availability of a resource, consider the fictional company SiteRequest. One of the servers at SiteRequest's Paris data center, serverWeb1, contains the main Web site content for the wide IP, www.siterequest.com. To ensure that this server is available, SiteRequest configures an HTTP monitor within the Global Traffic Manager and assigns it to serverWeb1. This monitor periodically accesses the server to verify that the main index.html page is available. If the monitor cannot access the page, it notifies the Global Traffic Manager, which then considers the server unavailable until the monitor is successful.

Monitors provide a robust, customizable means of determining the availability of a given resource with the Global Traffic Manager. The following procedure describes how to control the impact that a set of monitors has on the availability of a resource.

For more detailed information on the types of monitors available to the Global Traffic Manager and how to configure them, see Chapter 10, Configuring Monitors .

To control how monitors determine the availability of a virtual server

  1. On the Main tab of the navigation pane, expand Global Traffic and then click Servers.
    The main screen for servers opens.
  2. Click the name of the server that contains the virtual server you want to configure.
    The properties screen for the server appears.
  3. On the menu bar, click Virtual Servers.
    The virtual server screen opens.
  4. Click the name of the virtual server that you want to configure.
    The properties screen for the virtual server appears.
  5. From the Configuration list, select Advanced.
    This displays additional fields, and allows you to modify additional default settings.
  6. Determine the availability requirements for the virtual server:
    • If you want the Global Traffic Manager to consider the virtual server only if all monitors assigned to the virtual server are successful, select All Health Monitors from the Availability Requirements list.
    • If you want the Global Traffic Manager to consider the virtual server as available only if some monitors assigned to it are successful, select At Least from the Availability Requirements list. When you select At Least, a box appears where you can type the number of monitors that must be successful for the virtual server to be available.
  7. Click the Update button to save your changes.

You can also assign monitors to a specific server. In most cases, when you assign a monitor to a server, that monitor checks all virtual servers associated with that server.

An exception to this guideline is the SNMP monitor. If you assign an SNMP monitor to a Cisco, Alteon, Extreme, Foundry, or Radware server, that monitor obtains information on the virtual servers associated with that server. If you assign the SNMP monitor to any other server type, that monitor obtains data on the server itself.

For more information on the SNMP monitor, see Chapter 10, Configuring Monitors .

In cases where you assign a monitor to a virtual server both directly and to its parent server, the availability information acquired from the monitor directly assigned to the virtual server takes precedence over any other data.

To assign a monitor to check virtual servers associated with a server

  1. On the Main tab of the navigation pane, expand Global Traffic and then click Servers.
    The main screen for servers opens.
  2. Click the name of the server that you want to configure.
    The properties screen for the server appears.
  3. From the Configuration list, select Advanced.
    This displays additional fields, and allows you to modify additional default settings.
  4. Determine the availability requirements for the virtual servers:
    • If you want the Global Traffic Manager to consider a virtual server only if all monitors assigned to the virtual server are successful, select All Health Monitors from the Availability Requirements list.
    • If you want the Global Traffic Manager to consider the virtual server as available only if some monitors assigned to it are successful, select At Least from the Availability Requirements list. When you select At Least, a box appears where you can type the number of monitors that must be successful for the virtual server to be available.
  5. Click the Update button to save your changes.

To control how monitors determine the availability of a pool

  1. On the Main tab of the navigation pane, expand Global Traffic and then click Pools.
    The main screen for pools opens.
  2. Click the name of the pool that you want to configure.
    The properties screen for the pool appears.
  3. From the Configuration list, select Advanced.
    This displays additional fields, and allows you to modify additional default settings.
  4. Determine the availability requirements for the pool:
    • If you want the Global Traffic Manager to consider the pool only if all monitors assigned to the pool are successful, select All Health Monitors from the Availability Requirements list.
    • If you want the Global Traffic Manager to consider the pool as available only if some monitors assigned to it are successful, select At Least from the Availability Requirements list. When you select At Least, a box appears where you can type the number of monitors that must be successful for the pool to be available.
  5. Click the Update button to save your changes.

To control how monitors determine the availability of a link

  1. On the Main tab of the navigation pane, expand Global Traffic and then click Links.
    The main screen for links opens.
  2. Click the name of the link that you want to configure.
    The properties screen for the link appears.
  3. From the Configuration list, select Advanced.
    This displays additional fields, and allows you to modify additional default settings.
  4. Determine the availability requirements for the link:
    • If you want the Global Traffic Manager to consider the link only if all monitors assigned to the link are successful, select All Health Monitors from the Availability Requirements list.
    • If you want the Global Traffic Manager to consider the link as available only if some monitors assigned to it are successful, select At Least from the Availability Requirements list. When you select At Least, a box appears where you can type the number of monitors that must be successful for the link to be available.
  5. Click the Update button to save your changes.

Managing dependencies for virtual servers

Within the Global Traffic Manager, you can configure a virtual server to be dependent on one or more virtual servers. In such a configuration, the virtual server is available only if all of the resources in its Dependency List are available as well.

For an example of virtual server dependencies, consider the fictional company SiteRequest. One of the servers, serverMain, at the Tokyo data center has two virtual servers: vsContact, which points to the contacts page of SiteRequest's Web site, and vsMail, which points to their mail system. The vsContact virtual server has vsMail added in its Dependency List. As a result, the Global Traffic Manager considers the vsContact virtual server available only if the vsMail virtual server is also available.

Setting virtual server dependencies

You can set dependencies for a virtual server at any time.

To set the dependency of a virtual server

  1. On the Main tab of the navigation pane, expand Global Traffic and then click Servers.
    The main screen for servers opens.
  2. Click the name of the server that contains the virtual server you want to configure.
    The properties screen for the server appears.
  3. On the menu bar, click Virtual Servers.
    The virtual server screen opens.
  4. Click the name of the virtual server that you want to configure.
    The properties screen for the virtual server appears.
  5. From the Configuration list, select Advanced.
    This displays additional fields, and allows you to modify additional default settings.
  6. In the Dependency List option, select a virtual server from the Server list and click Add.
    The virtual server appears as part of the Dependency List.
  7. Add additional virtual servers as needed.
  8. Click the Update button to save your changes.

Removing virtual server dependencies

You can remove a virtual server from another virtual server's Dependency List at any time.

To remove a virtual server from a Dependency List

  1. On the Main tab of the navigation pane, expand Global Traffic and then click Servers.
    The main screen for servers opens.
  2. Click the name of the server that contains the virtual server you want to configure.
    The properties screen for the server opens.
  3. On the menu bar, click Virtual Servers.
    The virtual server screen opens.
  4. Click the name of the virtual server that you want to configure.
    The properties screen for the virtual server opens.
  5. From the Configuration list, select Advanced.
    This displays additional fields, and allows you to modify additional default settings.
  6. In the Dependency List option, select a virtual server from the Dependency List and click Remove.
  7. Remove additional virtual servers as needed.
  8. Click the Update button to save your changes.

Organizing virtual server dependencies

When you configure the Dependency List option for a virtual server, the Global Traffic Manager checks each virtual server in the order in which you added them to the Configuration utility. You can change this order at any time.

To organize virtual server dependencies

  1. On the Main tab of the navigation pane, expand Global Traffic and then click Servers.
    The main screen for servers opens.
  2. Click the name of the server that contains the virtual server you want to configure.
    The properties screen for the server appears.
  3. On the menu bar, click Virtual Servers.
    The virtual server screen opens.
  4. Click the name of the virtual server that you want to configure.
    The properties screen for the virtual server appears.
  5. From the Configuration list, select Advanced.
    This displays additional fields, and allows you to modify additional default settings.
  6. In the Dependency List option, use the buttons provided to move the listed virtual servers up or down in the list.
  7. Click the Update button to save your changes.

Resuming connections to resources

When a network resource, such as a virtual server, goes offline, the Global Traffic Manager considers that resource to be unavailable and proceeds to send name resolution requests to other resources based on the configured load balancing mode. By default, the Global Traffic Manager resumes sending requests to an offline resource as soon as that the resource becomes available again, provided that the resource meets the appropriate load balancing requirements.

Under certain circumstances, you might not want the Global Traffic Manager to resume connections to a resource immediately. For example, a server for the fictional company, SiteRequest, goes offline. The Global Traffic Manager detects that the virtual servers associated with this server are unavailable, and proceeds to send name resolution requests to other virtual servers as appropriate. When the server is online again, it must still run several synchronization processes before it is fully ready to handle name resolution requests. However, the Global Traffic Manager might detect that the server is available before these processes are complete, and send requests to the server before that server can handle them.

To avoid this possibility, you can configure pools to use the manual resume feature. The manual resume feature ensures that the Global Traffic Manager does not load balance requests to a virtual server within a pool until you manually re-enable it.

To activate the manual resume feature

  1. On the Main tab of the navigation pane, expand Global Traffic and then click Pools.
    The main pools screen opens.
  2. Click the name of the pool.
    The properties screen of the pool opens.
  3. From the Configuration list, select Advanced.
    This displays additional fields, and allows you to modify additional default settings.
  4. Check Manual Resume.
  5. Click the Update button to save your changes.

Establishing persistent connections

Most load balancing modes divide name resolution requests among available pools or virtual servers. Each time the Global Traffic Manager receives a request, it sends that request to the most appropriate resource. For example, when a user visits a web site it results in multiple name resolution requests as that user moves from page to page. Depending on the load balancing mode selected, the Global Traffic Manager could send each request to a completely different virtual server, server, or even data center.

In certain circumstances, you might want to ensure that a user remains with a given set of resources throughout the session. For example, a user attempting to conduct a transaction through an online bank needs to remain with the same set of resources to ensure the transaction is completed successfully.

To ensure that users stay with a specific set of resources, the Global Traffic Manager includes a persistence option. The persistence option instructs the Global Traffic Manager to send a user to the same set of resources until a specified period of time has elapsed.

To establish persistent connections to a wide IP

  1. On the Main tab of the navigation pane, expand Global Traffic and then click Wide IPs.
    The main wide IP screen opens.
  2. Click the name of the wide IP.
    The Properties screen for the wide IP opens.
  3. On the menu bar, click Pools.
    The Pools List screen opens.
  4. From the Persistence list, select Enabled.
    A new option, Persistent TTL, appears in which you can state how long a connection should persist to the same resources.
  5. In the Persistent TTL box, type the time-to-live value, in seconds.
  6. Click the Update button to save your changes.

Draining persistent requests

If you elect to use persistent connections with your load balancing mode, you must decide how to handle connection requests when you need to take a specific pool of virtual servers offline. By default, the Global Traffic Manager immediately sends connection requests to other pools when you take that pool offline, even if you enabled persistent connections. In some situations, this behavior might not be desirable. For example, consider an online store. You might need to take a pool of virtual servers for this store offline; however, you do not want to interrupt shoppers currently purchasing any products. In this situation, you want to drain persistent requests. Draining requests refers to allowing existing sessions to continue accessing a specific set of resources while disallowing new connections. In the Global Traffic Manager, you configure this capability through the Drain Persistent Requests option.

Note

The Drain Persistent Requests option applies only when you manually disable the pool. It does not apply when the pool becomes offline for any other reason.

To drain persistent requests

  1. On the Main tab of the navigation pane, expand System and then click General Properties.
    The general properties screen opens.
  2. From the Global Traffic menu, choose General.
    The General Global Properties screen opens.
  3. Check Drain Persistent Requests.
  4. Click the Update button to save your changes.

Setting the last resort pool

When the Global Traffic Manager load balances name resolution requests, it considers any pool associated with a given wide IP as a potential resource. You can, however, modify this behavior by creating a last resort pool. A last resort pool is a pool of virtual servers to which the Global Traffic Manager sends connection requests in the event that all other pools are unavailable.

It is important to remember that any pool you assign as the last resort pool is not a part of the normal load balancing operations of the Global Traffic Manager. Instead, this pool is kept in reserve. The Global Traffic Manager uses the resources included in this pool only if no other resources are available to handle the name resolution request.

To set the last resort pool

  1. On the Main tab of the navigation pane, expand Global Traffic and then click Wide IPs.
    The main wide IP screen opens.
  2. On the menu bar, click Pools.
    The pools screen opens. This screen contains a list of the pools currently assigned to the wide IP.
  3. Click the Manage button.
    The manage pools screen opens.
  4. From the Last Resort Pool list, select a pool to be used as the last resort pool.
  5. Click the Update button to save your changes.



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