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This chapter and the next, "Deploying Web Site Content on an Internet CDN," describe the following processes, which you must complete to prepare your web site for a CDN deployment:
As a content provider, your organization delivers high value, high-bandwidth content to your customers or staff over an intranet or the public Internet. You may be a corporation that wants to offer live, streamed broadcasts of its CEO's quarterly earnings announcements to employees at their desktops, or you may be a public university that needs to deliver classroom content to distance learners in remote locations.
Whatever your business, you need a reliable, fast, and efficient means to deliver high-bandwidth web content to end users. To do this, you have likely turned to an outside "service provider" organization to help you manage your content distribution. That service provider has chosen the Cisco Internet Content Delivery Network (CDN) Software to manage the distribution of content to your users.
This chapter is designed to help you understand more fully the delineation of your responsibilities in deploying your CDN solution, as well as those of your service provider.
With the necessary technology infrastructure and the expertise on-staff to maintain and fine-tune the Cisco CDN hardware and software, your service provider handles day to day maintenance of your CDN.
However, some of the work of deploying your web site content on a CDN rests with you, the content provider. This work involves:
1. Coordinating with your service provider to create the DNS subdomains of your domain on which CDN content will reside. This includes assigning authoritative DNS control of your CDN subdomains to the content routers that will direct user requests to Content Engines.
2. Configuring origin content servers for live streaming. (Optional.)
3. Identifying content on your web site that needs to be pre-positioned or on-demand cached on your CDN hosted domain.
4. Changing the URLs of content you want cached to point to your CDN hosted domain.
5. Generating a manifest file that identifies the web site content you wish to pre-position on your CDN.
6. Notifying your service provider of the name and location of a manifest file for deployment on your designated hosted domain.
7. Monitoring content freshness after deployment.
With the help of the Cisco Internet CDN solution, selected content from your web site is mirrored on one or more CDN subdomains referred to as hosted domains. Each of these hosted domains is a subdomain in the DNS tree where clients make DNS resolution requests to CDN-controlled Content Routers.
Hosted domains use a subdomain name that is related to your web site's domain name. For example, if your web site DNS address is:
Users might access a copy of your web site from the following accelerated CDN hosted domain:
Each hosted domain contains a collection of cached or pre-positioned video-on-demand content that can be served from Content Engines deployed throughout your CDN. Your organization may be deploying one or more CDN-enhanced hosted domains—each corresponding to a different DNS subdomain—at once.
The following section explains how to modify a DNS server to create a CDN subdomain and explains the various options available to you, as a content provider, in deploying a CDN subdomain for your web page.
CDN hosted domains are created when you modify your web site's DNS tree to create one or more new subdomains to host CDN content. Each subdomain must be delegated to the Content Routers responsible for managing user requests on the CDN.
Refer to the following guidelines when creating a subdomain for use with the Cisco Internet CDN Software:
1. The hosted domain name must be a valid subdomain name. For example:
www.cdn.cisco.com
a. The first part of the domain name (www in this example) is open, and can be defined by you when you create the hosted domain name.
b. The remaining subdomain (the three segments after the first dot) must correspond to entries on your DNS server to provide a functional mapping for the CDN Content Routers that ultimately provide the appropriate DNS records.
2. The DNS server on which the subdomain is created must be given the right to act as the authoritative DNS server for the subdomain you specify.
3. The hosted domain name cannot contain underscore (_) characters.
Refer to the Cisco Internet CDN Software User's Guide or the documentation for your DNS server software for more information on creating subdomains or appending name server (NS) records.
After you have created the necessary DNS subdomains that will store your CDN content, your service provider can create the actual hosted domain using the CDN administrative software.
Using the CDN administrative interface, your service provider creates the hosted domain, assigns it a name, and associates it with the new DNS subdomain using the Content Distribution Manager graphical user interface.
Next, one or more Content Engines are assigned to the hosted domain using the Content Distribution Manager graphical user interface. Content Engines store the pre-positioned and cached content, then serve it to local users.
If you will be pre-positioning video on demand or live streamed content, your service provider must also link the hosted domain to a manifest file you have created.
See the "Pre-Positioning Web Site Content" section for instructions on creating a manifest file that identifies the web site content you want to pre-position and the "On-Demand Caching Web Site Content" section for instructions on modifying content URLs to cache web site content on your CDN hosted domain.
If you will be hosting live content on your CDN, you may need to modify the configuration of your live content servers. Currently, the Cisco Internet CDN Software supports live broadcasts from the following platforms:
See the "Configuring Origin Server for Live Streaming" section for detailed instructions on modifying your origin servers for live streaming over the CDN.
Your web site contains a variety of content types, from static image files in GIF or JPG format, to external documents, maybe in Adobe PDF format, to live content streamed by RealServer or Windows Media Services.
As part of the process of preparing your website for deployment on a CDN, you must decide which of this content you want to have accessed from your CDN and which will continue to be accessed and served from your web servers.
There are two options for deploying content. These options are not mutually exclusive; both can be used to deploy content on a hosted domain:
Each of these options is explained, in detail, in the sections that follow.
After your hosted domain has been created and content has been pre-positioned on it, you are ready to change your web site's content URLs to point to the new hosted domain address supplied by your service provider.
See the "Caching Content on Your CDN" section for instructions on modifying your web site's content URLs to point to your CDN.
To pre-position content, you must:
As the content provider, you are responsible for compiling a list of the content you want to deploy on the CDN and providing that list to your CDN administrator in the form of an XML-format manifest file.
The easiest way to generate a list of content on your web site is to create an automated script that "crawls" your entire web site (or as much of it as you want to be crawled) and identifies content that needs to be pre-positioned on the CDN based on rules you provide.
Cisco provides a free PERL script, Spider, you can use as a template for the creation of your spider script. When run, Spider outputs a database of web site content, based on rules you supply in a separate configuration file, that can be used to build a functioning manifest file in a fraction of the time it would take to author a manifest file by hand.
See the "Pre-Positioning Web Site Content" section as well as "Listing Web Site Content Using the Spider Script" section for instructions on identifying content to place on your CDN.
The easiest way to generate a manifest file that lists the content you want to pre-position is to create an automated script that builds the manifest, based on the data generated by the Spider script.
Cisco provides a free PERL script, Manifest, that you can use as a template for your own script. When run, Manifest outputs a valid, CDN manifest file based on the database of web site content generated by the Spider script and content rules that you supply in a separate configuration file.
See the "About the Manifest File" section for more information on the manifest file. Then see the "Creating a Manifest File" section to create your manifest file. Detailed information on the Manifest script can be found in the "Selecting Live and Pre-position Content Using the Manifest Script" section.
One of the primary concerns you will have once you have deployed your content on a Cisco Internet CDN is controlling content freshness: making sure that users are accessing up-to-date content from CDN caches, and making sure that updated material is quickly disseminated throughout the CDN.
Because you create and maintain the manifest file and host it on your web server, you can determine when any content item is refreshed.
The frequency with which individual content items on the CDN are refreshed is controlled using the both the expires and ttl (Time to Live) attributes in the manifest file.
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Note The default ttl time can be modified by your service provider using the Content Distribution Manager administrative interface. Please consult with your service provider if you would like to change the default ttl value. |
As content is changed and updated on your origin server, it will also be updated on the CDN at an interval represented by the ttl attribute. Keep in mind, however, that the ttl attribute represents the minimum time in which the content will be updated. Depending on the volume of content that must be refreshed at any given time and the file size of the piece of content that must be refreshed, it could take longer than the interval specified by the ttl attribute to refresh any one piece of content.
See the "Manifest File Structure and Syntax" section for information on using the expires and ttl attributes.
While the expires and ttl attributes are the most common methods for controlling the freshness of individual content items that are named in the manifest file and that have been updated, if you will be making a large number of changes to your manifest file, you may want to update, or re-fetch, the entire manifest.
Fetching is initiated from the Content Distribution Manager administrative interface. Coordinate with the operations person at your service provider organization to re-fetch the manifest for your hosted domain(s).
Content that is only partially fetched from your origin server is not added to the CDN and will not be served from you hosted domain. See the "Verifying Content Freshness"section next for information on how content freshness and replication status is monitored by your service provider.
The Cisco Internet CDN software provides a wealth of information to CDN administrators on the status of content replication and freshness through a variety of logging mechanisms.
From the Content Distribution Manager administrative interface, your service provider can verify whether content replication to a hosted domain was successful.
To verify if a piece of content has been refreshed, your service provider will look at manifest log files that reside on each Content Engine belonging to your hosted domain. Within that log file are entries pertaining to each content item on the hosted domain. Your operations person will want to look for log entries pertaining to the particular content file name and verify that it was successfully imported to or refreshed on the hosted domain.
In the event that errors were encountered during replication, either because the disk space allocation for the hosted domain content was exceeded, or because replication failed for a particular content item, your service provider has a number of tools available to them to correct the problem, including allocating more disk space for the hosted domain and re-fetching the manifest file. In the event that a corrupt content item is causing problems, your service provider may ask you to remove references to that content from your website or manifest file. See the "Obsoleting Bad Content" section next for more information on removing bad content from your hosted domain.
Because access to the CDN log files requires direct access to CDN devices, much of this logging is transparent to you as a content provider. Coordinate with your service provider regarding content updates.
If you have accidentally positioned a bad content item on your hosted domain with an expiration date in the distant future, you can remove that content. Do so by revising your content URL or your manifest file to omit the reference to the damaged content item. If you need to update your manifest file, remember to ask your service provider to re-fetch the manifest file. The bad content item will no longer be accessible from the CDN because it is not named in the manifest and the disk space allocated by the obsoleted content item will be reallocated for valid content.
See the "Creating a Manifest File" section for instructions on creating your manifest file.
Posted: Tue Oct 1 04:13:02 PDT 2002
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