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Fastly Edge SDK

Our network is designed to provide fast, real-time digital experiences. Built on a highly customized version of Varnish, we use Varnish Configuration Language (VCL) and a global network of powerful servers to deliver intelligent caching and application logic at the edge.

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Varnish & VCL

We use a highly customized version of Varnish to perform intelligent caching and push application logic to the edge. Our Custom Varnish Configuration Language (VCL) allows you to control most aspects of an HTTP request or response, including where content is fetched from, what’s cached, and how it’s cached and served.

Our powerful control panel and configuration API auto generate VCL for you. You can also write your own VCL, upload it alongside ours, and activate instantly. Fastly Support Plans and Professional Services Packages provide configuration assistance for more complex setups.

Varnish & VCL

Edge modules

Our Edge Modules leverage VCL to perform custom logic at the edge, closer to your users. You can tailor how content is served for the best possible user experience.

  • Edge Authorization / Paywalls authorize requests faster by placing access at the edge rather than sending requests to your origin and back again.
  • Location Detection identifies where customer requests are coming from, so you can offer customized experiences based on location. For example, you can create a virtual boundary (geo-fencing) and send customers within that boundary localized content such as coupons or special offers.
  • Mobile Device Detection helps you determine what device a customer is using, so you can tailor content served; e.g. for iPhone users, you can serve a mobile optimized version of your pages.
  • Visitor Prioritization gives priority to active buyers if your site becomes overloaded during peak traffic events, directing casual shoppers to a waiting room.
  • Edge Side Include (ESI) is a Varnish feature which accelerates site performance by allowing you to mix both cacheable and uncacheable content. Fastly serves cacheable content and sends requests for uncacheable content — such as the shopping cart — back to origin.

Edge Dictionaries

Fastly Edge Dictionaries — key-value pairs that your VCL can reference inside your Fastly service (like a database at the edge) — offer flexibility and control at the network edge, letting you make real-time decisions from every server in our network. Using an API call, you can add or update data inside an Edge Dictionary any time, without having to deploy a new version of your service.

Edge Dictionaries enable content sharing and social media outlets to update large referrer spam blacklists in real time. Image providers can quickly perform token checks for certain objects. Adtech companies can block bad actors at the edge, while global publishers can redirect users to a country site based on geolocation.

Edge Dictionaries