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Manual Chapter: Controlling Load Balancing Costs
Manual Chapter
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8
The BIG-IP® Link Controller provides a variety of methods for managing the traffic flowing in and out of a network. A common method is cost-based load balancing. In cost-based load balancing, you prioritize link usage based on the cost of the bandwidth for that connection to the Internet. The Link Controller sends traffic to the link that is currently operating at the lowest cost. As the usage cost for each link changes, the Link Controller dynamically shifts traffic to the best link.
Weighting
The Weighting option for each link determines how the Link Controller prioritizes the links in its configuration. By default, this option is set to Ratio, which is applicable for both ratio load balancing and bandwidth load balancing. For cost-based load balancing, however, you must set this option to Price (Dynamic Ratio).
Prepaid Segment
Most Internet Service Providers (ISPs) offer bandwidth plans that include a prepaid amount of bandwidth. In the Prepaid Segment option, you assign the appropriate bandwidth and cost values that are prepaid for the link.
Incremental Segments
The Incremental Segment option allows you to define the cost per segment values that apply to this link. You can assign as many incremental segments as needed.
Note: When implementing cost-based load balancing, it is important that your configuration applies to all of the links that the Link Controller manages. For example, F5 Networks does not recommend applying cost-based load balancing to one set of links and ratio load balancing to another set.
In this process, shown in Figure 8.1, the following sequence occurs:
3.
The Link Controller determines the best link based on current cost estimates and bandwidth usage, and sends the appropriate response back to the LDNS server.
5.
The client then communicates with the appropriate virtual server through the corresponding link that the Link Controller specified.
To illustrate how cost-based load balancing works, consider the fictional company SiteRequest. This company has two links for managing its inbound and outbound traffic:
Link Alpha, which is the primary link for the network. This link uses an ISP to which a flat fee of $45 is paid for up to 4Mbps of total (both inbound and outbound) traffic. If the limit of 4Mbps is exceeded, SiteRequest incurs a $2/Mbps charge.
Link Beta, which is a secondary link for the network. This link uses an ISP with which SiteRequest does not have a prepaid amount of bandwidth. Instead, SiteRequest is billed based on a pay-as-you-go basis. The rate charged for using this link is set at $1/Mbps.
As these rates illustrate, the most cost-efficient configuration for SiteRequests links is to have Link Alpha handle traffic until it reaches 4Mbps, then send any traffic over 4Mbps to Link Beta. When the traffic decreases, the Link Controller must switch back to using only Link Alpha again.
Table 8.1 provides additional information about each link.
Router Address
Uplink Address
The first task in designing a Link Controller configuration that uses cost-based load balancing to manage outbound traffic is to add and configure the links into the Link Controller. You can configure each link using a variety of options; however, the critical settings are the Weighting, Prepaid Segment, and Incremental Segment options, with which you set the pricing values for the link.
Note: The following procedure applies to the Link Controller system; however you can also use this procedure if you have a Global Traffic Manager. If you are configuring links on a Global Traffic Manager, you must first create a data center, to which you then assign the configured link.
1.
On the Main tab of the navigation pane, expand Link Controller, and then click Links.
2.
Click Create.
3.
In the Name box, type the name of the link.
For this example, type Link Alpha.
4.
In the Router Address box, type the IP address of the router in the Address box.
For this example, type 192.168.5.5.
5.
In the Uplink Address box, type the IP address that corresponds with the external Internet connection.
For this example, type 192.168.5.6.
6.
In the Service Provider box, type the name of the ISP provider.
For this example, select Global ISP.
7.
From the Configuration list, select Advanced.
8.
From the Weighting list, select Price (Dynamic Ratio).
9.
In the Prepaid Segment box, type the amount of bandwidth that is prepaid for the link.
For this example, type 4000.
10.
In the Incremental Segments area, add the incremental segment price.
For this example type the following entry:
Up to 1000 bps at 2 $/Mbps
11.
Click Create.
Repeat this procedure to add the second link to the configuration. In this example, when you add the second link, set the Prepaid Segment option to 0 and add the following entry in the Incremental Segment option:
After you have added and configured the relevant links, the next task in implementing cost-based load balancing is to create the default gateway pool that will load balance the traffic across the links.
1.
On the Main tab of the navigation pane, expand Local Traffic and then click Pools.
2.
Click Create.
3.
In the Name box, type the name of the pool.
For this example, type default_gateway_pool.
4.
For the New Members setting, add the IP addresses associated with each link.
In this example type the following:
5.
Click Finished.
After you create a default gateway pool, you must instruct the Link Controller to use the pool as the default gateway connection between the internal network and the Internet.
1.
2.
Click Add.
3.
From the Type list, select Default Gateway.
4.
From the Resource list, select Use Pool.
5.
From the Pool list, select default_gateway_pool.
6.
Click Finished.
After creating the pools, you configure the virtual servers, one for each link that load balances inbound connections across the servers. You also configure one wildcard virtual server to load balance outbound connections across the routers.
VS for Link Alpha 1, which has an IP address of 10.10.5.5:80 and represents a single host on the network.
VS for Link Alpha 2, which has an IP address of 10.10.5.6:80 and represents a single host on the network.
VS for Link Beta 1, which has an IP address of 10.10.10.5:80 and also represents a single host on the network.
VS for Link Beta 2, which has an IP address of 10.10.10.6:80 and also represents a single host on the network.
1.
On the Main tab of the navigation pane, expand Local Traffic and then click Virtual Servers.
2.
Click Create.
3.
In the Name box, type the name of the virtual server.
For this example, type VS for Link Alpha 1.
4.
In the Destination area, select Host.
5.
In the Service Port box, type 80.
6.
Click Finished.
Repeat this procedure for the additional virtual servers. Once the remaining virtual servers are in the configuration, you can define the wildcard virtual server.
1.
On the Main tab of the navigation pane, expand Local Traffic and then click Virtual Servers.
2.
Click Create.
For the service port, type 0 or select any from the list.
4.
Click Finished.
To complete the link load balancing configuration, you must configure a wide IP for each pair of virtual servers you created for each link. Each wide IP in the configuration has a set of virtual servers to which the Link Controller load balances incoming DNS requests. The wide IP is made up of only virtual servers that the Link Controller manages. When you configure the wide IP, you also specify the load balancing methods that the Link Controller applies to the incoming DNS requests.
For this implementation, you use the wide IP www.siterequest.com, using the Global Availability as the preferred load balancing method, and None for the Alternate and Fallback methods.
1.
On the Main tab of the navigation pane, expand Link Controller and then click Inbound Wide IPs.
2.
Click Create.
3.
In the Name box, type the name of the wide IP
For this example, type www.siterequest.com.
4.
In the Load Balancing Method area:
Select Ratio from the Preferred list.
Select Round Robin from the Alternate list.
Select Return to DNS from the Fallback list.
5.
In the Member List area, add the virtual servers that you created in the previous Configuring the virtual servers.
6.
Click Finished.
At this point, you now have a Link Controller configured to manage DNS traffic for www.siterequest.com. As data flows in and out of the network, the Link Controller monitors the total amount of bandwidth for each link. While traffic remains below 4Mbps, the Link Controller uses Link Alpha. If traffic exceeds that amount, the Link Controller sends the overflow traffic to Link Beta. And, should a link go offline for any reason, the Link Controller uses the Alternate and Fallback load balancing modes to route traffic through an available link.
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