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Archived Manual Chapter: 3-DNS Admin Guide, v4.6.2: Configuring a Content Delivery Network
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7

Configuring a Content Delivery Network



Introducing the content delivery network

A content delivery network (CDN) is a network of clusters that includes devices designed and configured to maximize the speed at which a content provider's content is delivered. The purpose and goal of a content delivery network is to cache content closer, in Internet terms, to the user than the origin site is. Using a CDN to deliver content greatly reduces wide area network (WAN) latency so the content gets to the user more quickly, and the origin site servers are not overloaded and slowed by requests for content. The fundamental WAN traffic distribution mechanism in all CDNs that we know about is DNS.


Using the 3-DNS Controller in a CDN

The following features make the 3-DNS Controller a logical choice for the wide-area traffic management in a CDN.

  • CDN switching
    CDN switching is the functionality of the 3-DNS Controller that allows a user to delegate global traffic to a third-party network. The two features of the 3-DNS Controller that make CDN switching possible are:

    • Geographic redirection
      The 3-DNS Controller uses the Topology load balancing mode to redirect DNS requests based on location information derived from the DNS query message. You can set up wide IPs so that the 3-DNS Controller delegates DNS queries either to a data center, by responding with A records, or to a CDN provider, by responding with a CNAME record.

    • CDN providers
      We have partnered with several CDN providers to facilitate usage of CDNs. To take advantage of these content delivery partnerships, you can designate a pool type CNAME on the 3-DNS Controller so that the 3-DNS Controller redirects requests to a CDN provider's name servers rather than to a grouping of virtual servers. For a list of our partner CDN providers, click CDN Providers on the 3-DNS Controller home screen.

  • Resource monitoring, limits, and thresholds
    The 3-DNS Controller has sophisticated monitoring screens so you can quickly analyze the performance and availability of your network resources. You can also set limits on physical and throughput resources to ensure that your content is always available and none of your resources are overtaxed.


Reviewing a sample CDN configuration

The two following diagrams illustrate how DNS query resolutions for content delivery networks are processed by the 3-DNS Controller. In the example, the content provider for www.download.siterequest.com has two data centers, one in San Jose, California (see Figure 7.1 ), and one in Washington, DC (see Figure 7.2 ). The 3-DNS Controllers (in the two data centers) use the Topology load balancing mode to direct the DNS queries to the geographically closest virtual servers.

In Figure 7.1 , a local DNS server in Seattle, Washington, sends a query for the domain www.download.siterequest.com (1A). Based on the location information in the query packet header, the 3-DNS Controller in the content provider's North American data center resolves the query to the best virtual server in that data center, and sends an A record response to the Seattle LDNS (1B).

 


Figure 7.1 DNS query resolution based on Topology load balancing mode

In Figure 7.2 , a local DNS server in London sends a query for the same domain, www.download.siterequest.com (2A). Based on the location information in the query packet header, the 3-DNS Controller in the content provider's North American data center responds to the London LDNS with delegation information (a CNAME record) about the DNS for the content delivery peer (2B). The London LDNS then sends the redirected query (based on the CNAME record) for www.download.siterequest.com to the CDN provider (2C). The CDN provider's DNS server responds with the IP address of the best virtual server for resolution among those in the CDN (2D). The CDN provider's cache servers resolve to the origin site virtual servers for cache refreshes using a different domain name (origin.download.siterequest.com).

 


Figure 7.2 DNS query resolution to content delivery network provider


Deciding to use a CDN provider

The 3-DNS Controller is well-suited to serve as the wide-area traffic manager (WATM) for CDNs that have many of the following attributes:

  • The CDN provider has a global presence around the edge of the Internet.

  • The CDN provider outsources a content delivery infrastructure to content providers.

  • The CDN provider is the authoritative DNS for the content provider's domain, and uses DNS to find a data center with CDN resources at the edge of the network nearest to the client.

  • The CDN provider serves all of the content provider's traffic because the CDN is authoritative for the content provider's domain. Content providers manage this by creating logical groupings of their content under different domains. For example, an investment firm might have a CDN host their news content at news.domain.cdn.net, while they serve their stock quotes content with quote.siterequest.com from their corporate data center.

  • The CDN provider sets its billing rates based on megabits per second. The CDN provider determines billing by collecting and processing edge cache and server logs.

  • The CDN provider has an infrastructure in place to manage the multitude of geographically distributed devices.

  • The CDN provider usually establishes some type of service level agreement (SLA) to ensure that content is being served faster from the CDN than from the content provider's origin servers.


Setting up a CDN provider configuration

The following sections describe the specific tasks you perform to set up a CDN provider configuration, as shown in the example configuration . The tasks are as follows:

  • Adding data centers

  • Adding 3-DNS Controllers

  • Adding load balancing servers

  • Adding wide IPs and pools

  • Adding a topology statement


Adding data centers

The first task you perform is to add the data centers to the configuration on the 3-DNS Controller.

To add data centers using the Configuration utility

  1. In the navigation pane, click Data Centers.
    The Data Centers screen opens.

  2. Click Add Data Center on the toolbar.
    The Add Data Centers screen opens.

  3. Add the data center information. For our example, we add the two data centers labeled Data Center 1 and Data Center 2.

  4. Repeat the previous steps to add all of your data centers to the configuration.


Adding 3-DNS Controllers

Once you have added all of your data centers to the 3-DNS configuration, you are ready to advise the 3-DNS Controller you are configuring about other 3-DNS Controllers in your network.

To add 3-DNS Controllers using the Configuration utility

  1. In the navigation pane, expand the Servers item, then click 3-DNS.
    The 3-DNS List screen opens.

  2. Click Add 3-DNS on the toolbar.
    The Add New 3-DNS screen opens.

  3. Add the 3-DNS Controller information.

  4. Repeat the previous steps to add any additional 3-DNS Controllers to the configuration.

    Configuration note

    Please note that when you are working with more than one 3-DNS Controller, you create your entire configuration on one system and then add the second system using the 3dns_add script. The 3dns_add script copies the entire configuration from the first system onto the second system, and synchronizes all of the settings. For details on configuring additional 3-DNS Controllers in existing networks, using the 3dns_add script, see Chapter 10, Adding a 3-DNS Controller to an Existing Network .


Adding load balancing servers

Now you are ready to let the 3-DNS Controller know about any BIG-IP systems, EDGE-FX systems, or hosts that you have in your data centers. The servers and virtual servers that you add to this configuration are the servers that load balance your origin site content. For specific information on configuring any of these server types, please review Setting up servers .


Adding wide IPs and pools

Once you have added all the physical elements to the 3-DNS configuration, you can begin configuring wide IPs and pools for the CDN configuration. In addition to setting up the wide IPs and pools for your origin site, you also set up a pool for the CDN provider.

Before you start adding wide IPs, verify that you have configured all the virtual servers you need for load balancing for your origin site. The following instructions describe how to set up the CDN configuration shown in Figures 7.1 and 7.2 .

To add a wide IP and pool using the Configuration utility

  1. In the navigation pane, click Wide IPs.
    The Wide IP List screen opens.

  2. Click Add Wide IP on the toolbar.
    The Add a New Wide IP screen opens.

  3. Add the wide IP address, name, and port information. For our example, the wide IP name is www.download.siterequest.com.

  4. For the Pool LB Mode, select Topology and click Next.
    The Configure Load Balancing for New Pool screen opens.

  5. In the Configure Load Balancing for New Pool screen, update these settings:

    1. Add the pool name.
      For our example, the first pool name is origin.

    2. Check the Use Dynamic Ratio option.

    3. In the Load Balancing Modes, Preferred list, select Round Trip Time.

    4. In the Load Balancing Modes, Alternate list, select Packet Rate.

    5. In the Load Balancing Modes, Fallback list, select Round Robin.

    6. Accept the defaults for the rest of the settings and click Next.
      The Select Virtual Servers screen opens.

  6. In the Select Virtual Servers screen, check the virtual servers among which you want the 3-DNS Controller to load balance DNS requests, and click Finish.
    The 3-DNS Controller adds the wide IP and settings to the configuration. For our example, you would check the virtual servers that map to the download site content in the North American data center.

To add a CDN provider pool to the wide IP

     

  1. In the navigation pane, click Wide IPs.
    The Wide IP List screen opens.

  2. In the Wide IP List screen, click 1 Pools in the Pools column for the wide IP www.download.siterequest.com.
    The Modify Wide IP Pools screen opens.

  3. On the toolbar, click Add Pool.
    The Configure Load Balancing for New Pool opens.

  4. Update these settings:

    1. Add the pool name.
      For our example, the CDN provider pool name is cdn_pool.

    2. In the Pool TTL box, type 60. With a longer time-to-live, an LDNS has time to follow the CNAME record and redirect queries to the CDN.

    3. In the Dynamic Delegation, Type list, select CNAME.

    4. In the Dynamic Delegation, Canonical Name box, type the canonical name that you want the 3-DNS Controller to deliver in the CNAME record when it redirects traffic to the CDN provider. For our example, the canonical name is www.download.siterequest.cdn.net. Note that the canonical name for the CDN pool type automatically becomes an alias for the wide IP.

  5. Click Next.
    The Wide IP List screen opens.

    You have now set up the load balancing and delegation pools for your domain. The last required configuration step is to create a topology statement.


Adding a topology statement

The topology statement contains the topology records that the 3-DNS Controller uses to load balance DNS queries from geographically dispersed local DNS servers. The following procedure describes how to set up a topology statement, with two topology records, for our example.

Note


For more detailed information on working with topology on the 3-DNS Controller, see Chapter 3, Topology , in the 3-DNS Reference Guide . For information on setting up globally-distributed network with Topology load balancing, see Chapter 6, Configuring a Globally-Distributed Network , in this guide.

 

To set up topology records using the Configuration utility

  1. In the navigation pane, click Topology.
    The Manage Topology Records screen opens.

  2. For the first topology record, select Continent in the upper LDNS box.

  3. In the lower LDNS box, select North America.

  4. In the upper Server box, select Wide IP Pool.

  5. In the lower Server box, select origin.

  6. In the Weight box, type a value. For our example, we type 100.

  7. Click Add.
    The first topology record is added to the configuration.

  8. For the second topology record, in the upper LDNS box select Continent.

  9. In the lower LDNS box, select North America.

  10. Check the LDNS Not Equal box.

  11. In the upper Server box, select Wide IP Pool.

  12. In the lower Server box, select cdn_pool.

  13. In the Weight box, type a value. For our example, we type 100.

  14. Click Add.
    The second topology record is added to the configuration.

    Now you have created a topology statement for your CDN, and the 3-DNS Controller can successfully load balance DNS queries based on the location information derived from the DNS query message. For our example, using the topology statement you just created, the 3-DNS Controller would direct queries for www.download.siterequest.com that originated in North America to the origin pool for resolution. Requests that did not originate in North America would be directed to the CDN provider using the cdn_ pool.


Ensuring resource availability

The following resource availability settings are designed to ensure that your content is always available and that your system resources are not overtaxed to the point of failure. The resource availability settings you may want to use with your CDN configuration are:

  • Last resort pool
    You can designate a pool as the last resort pool so in the event that all other pools become unavailable for load balancing, the 3-DNS Controller can direct DNS queries to the virtual servers in this pool. For information on configuring a last resort pool, see Using the last resort pool designation in Chapter 2, Load Balancing , in the 3-DNS Reference Guide .

  • Limit settings
    You can set limits on system resources and throughput to enhance availability. You can set limits for any server type, virtual servers, and pools. For more information on setting limits, view the online help for the Modify Limit Settings screens in the Configuration utility.

  • ECV monitor
    With an extended content verification (ECV) monitor, you can verify that a specific file is available on the content servers for a wide IP. For more information on ECV monitors, refer to Working with the ECV service monitor, in the 3-DNS Reference Guide , Chapter 2, Load Balancing .


Monitoring the configuration

The following resources can help you monitor your configuration and troubleshoot problems.

  • You can view performance metrics, limit settings, and other details about your data centers, servers, virtual servers, wide IPs, and pools in the Statistics screens in the Configuration utility. For more information on specific Statistics screens, click Help on the toolbar.

  • You can view your configuration using the Network Map in the Configuration utility. You can also make modifications to the configuration from the Network Map. Click Help on the toolbar if you have questions on how to use the Network Map.

  • You can review detailed information on the specific features of the 3-DNS Controller in the 3-DNS Reference Guide .



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