Content and its delivery

Content types delivered by Fastly

The underlying protocol used by the World Wide Web to define how content is formatted and transmitted is called the Hypertext Transfer Protocol (HTTP). Fastly's CDN Service delivers all HTTP-based file content (e.g., HTML, GIF, JPEG, PNG, JavaScript, CSS) including the following:

  • Static content
  • Dynamic content
  • Video content

Each content type is described below.

Static content

Static content includes content that remains relatively unchanged. Fastly can control static content in two ways:

  • using the time to live (TTL) method, where Fastly's cache re-validates the content after expiration of the TTL, or
  • using Fastly's Instant Purge functionality, in which content remains valid until the cache receives a purge request that invalidates the content.

Examples of static content include images, CSS, and JavaScript files.

Dynamic content

Dynamic content includes content that changes at unpredictable intervals, but can still be cached for a fraction of time. We serve this dynamic content by taking advantage of Fastly's Instant Purge functionality. Using this functionality, dynamic content remains valid only until a Fastly cache receives a purge request that invalidates the content. Fastly understands that the rate of those purge requests cannot be predicted. Dynamic content may change frequently as a source application issues purge requests in rapid succession to keep the content up to date. Dynamic content can, however, remain valid for months if there are no changes requested.

Examples of dynamic content include sports scores, weather forecasts, breaking news, user-generated content, and current store item inventory.

Video content

Video content includes:

  • Live video streams
  • Video on Demand (VOD) content libraries

Video content can be served using standard HTTP requests. Specifically, Fastly supports HTTP Streaming standards, including HTTP Live Streaming (HLS), HTTP Dynamic Streaming (HDS), HTTP Smooth Streaming (HSS), and MPEG-DASH. For Fastly's CDN Service to deliver video, the video must be packaged.

Content sources supported by Fastly

Fastly caches deliver various types of content from many different sources. Supported sources include:

  • Websites
  • Internet APIs
  • Internet Applications
  • Live and Live Linear Video
  • Video on Demand (VOD) Libraries

Regardless of the content source, the content's source server must communicate using HTTP. HTTP defines specific types of methods that indicate the desired action to be performed on content. The manner in which those HTTP methods are used (the standard, primary methods being GET, POST, PUT, and DELETE) can be labeled as being RESTful or not. Fastly supports RESTful HTTP by default, but also can support the use of non-RESTful HTTP as long as the method used is mapped to its appropriate cache function. Each of the content sources supported by Fastly are described in more detail below.


Websites are servers that provide content to browser applications (e.g., Google's Chrome, Apple's Safari, Microsoft's Internet Explorer, Opera Software's Opera) when end users request that content. The content contains both the requested data and the formatting or display information the browser needs to present the data visually to the end user.

With no CDN services involved, browsers request data by sending HTTP GET requests that identify the data with a uniform resource locator (URL) address to the origin server that has access to the requested data. The server retrieves the data, then constructs and sends an HTTP response to the requestor. When a CDN Service is used, however, the HTTP requests go to the CDN rather than the origin server because the customer configures it to redirect all requests for data to the CDN instead. Customers do this by adding a CNAME or alias for their origin server that points to Fastly instead.

Internet APIs

Application program interfaces (APIs) serve as a language and message format that defines exactly how a program will interact with the rest of the world. APIs reside on HTTP servers. Unlike the responses from a website, content from APIs contain only requested data and identification information for that data; no formatting or display information is included. Typically the content serves as input to another computing process. If it must be displayed visually to an end user, a device application (such as, an iPad, Android device, or iPhone Weather application) does data display instead.

Legacy internet applications

Legacy internet applications refer to applications not originally developed for access over the internet. These applications may use HTTP in a non-RESTful manner. They can be incrementally accelerated without caching, benefiting only from the TCP Stack optimization done between edge Fastly POPs and the Shield POP, and the Shield POP to the origin. Then caching can be enabled incrementally, starting with the exchanges with the greatest user-experienced delay.

Live and live linear video streams & video on demand libraries

Live and live linear video content (for example, broadcast television) is generally delivered as a stream of information to users, which they either choose to watch or not during a specific broadcast time. Video on demand (VOD), on the other hand, allows end users to select and watch video content when they choose to, rather than having to watch at a specific broadcast time.

Regardless of which type of video content an end user experiences, a video player can begin playing before its entire contents have been completely transmitted. End users access the video content from a customer's servers via HTTP requests from a video player application that can be embedded as a part of a web browser. Unlike other types of website content, this content does not contain formatting or display information. The video player handles the formatting and display instead.

When the video content is requested, the customer's server sends the content as a series of pre-packaged file chunks along with a manifest file required by the player to properly present the video to the end user. The manifest lists the names of each file chunk. The video player application needs to receive the manifest file first in order to know the names of the video content chunks to request.

Pre-packaging in this context refers to the process of receiving the video contents, converting or transcoding the stream into segments (chunks) for presentation at a specific dimension and transmission rate, and then packaging it so a video player can identify and request the segments of the live video a user wants to view.

To request video delivery on your account, contact your Fastly Account Representative at

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