> ## Documentation Index
> Fetch the complete documentation index at: https://docs.gcore.com/llms.txt
> Use this file to discover all available pages before exploring further.

# FastEdge overview

FastEdge runs WebAssembly applications on Gcore's global edge network. Apps execute at the edge node closest to the request — no infrastructure to configure or maintain. Common use cases include A/B testing, personalization, authentication, and image processing.

## Application types

FastEdge supports two application types: HTTP and CDN. The application type determines how the application integrates with FastEdge and which setup guide to follow.

**Modern HTTP applications** receive and respond to HTTP requests directly. They implement the [WASI P2](https://wasi.dev/releases/wasi-p2) `wasi:http/proxy` interface — the current recommended standard for WebAssembly HTTP applications. Supported in Rust (via the `wstd` crate) and JavaScript. Use this type for new edge services: APIs, redirects, authentication proxies, and similar workloads.

**Legacy HTTP applications** also handle HTTP requests directly, but use Gcore's own `fastedge` crate rather than the WASI standard. They target [WASI P1](https://wasi.dev/releases/wasi-p1), the original WebAssembly system interface. Use it when maintaining existing applications built on the `fastedge` crate.

**CDN applications** run inside a CDN resource's request pipeline. They implement the [Proxy-Wasm](https://github.com/proxy-wasm/spec) specification — an open standard for WebAssembly-based proxy extensions — and can intercept traffic at four stages: on request headers, on request body, on response headers, and on response body. Supported in Rust and AssemblyScript. Use this type when extending an existing CDN-served site with edge logic.

To get started, choose the setup guide that matches the application type and language:

| App type    | Language   | Setup guide                                                         |
| ----------- | ---------- | ------------------------------------------------------------------- |
| Modern HTTP | Rust       | [Rust (Modern HTTP)](/fastedge/getting-started/setup-rust-modern)   |
| Modern HTTP | JavaScript | [JavaScript](/fastedge/getting-started/setup-javascript)            |
| Legacy HTTP | Rust       | [Rust (Legacy HTTP)](/fastedge/getting-started/setup-rust-legacy)   |
| CDN         | Rust       | [Rust (CDN / Proxy-Wasm)](/fastedge/getting-started/setup-rust-cdn) |

Both application types share the same deployment workflow:

1. Compile the application to WebAssembly and [upload the binary](/fastedge/getting-started/create-fastedge-apps) to FastEdge.
2. Gcore deploys it across edge nodes worldwide. Traffic is automatically routed and load-balanced.
3. When a request arrives, the runtime executes the application and returns the result to the client.

## Key benefits

* **Run code close to users.** FastEdge executes on the edge node closest to each request, reducing round-trip latency without relocating the origin.
* **Deploy without managing servers.** Gcore handles deployment, scaling, and routing across the global network. The application binary is the only artifact to maintain.
* **Isolated execution per application.** Each application runs in a WebAssembly sandbox, isolated from other applications on the same node.
* **Write in Rust or JavaScript.** Both languages have first-class SDK support. Rust covers both HTTP and CDN application types; JavaScript supports HTTP applications.

## Use cases

### A/B testing

Split traffic between application versions at the edge — by percentage, geolocation, subnet, or a combination. Teams test changes on a limited audience before a full rollout, with no changes to the origin required.

### Personalization

Serve region-specific content based on geolocation, IP address, or request headers — different language, currency, or product catalog per market — without modifying the origin application.

### Authentication

Validate JWT tokens at the edge before a request reaches the origin. The origin processes only validated requests, reducing its load and eliminating a network round-trip for invalid ones.

### Image manipulation

Convert images at the edge node closest to the request — bulk WebP conversion, low-resolution resizing, watermarking — rather than at a central origin, reducing bandwidth and processing load.

### URL rewriting and header control

Rewrite non-human-readable CMS URLs to a user-friendly format in the response, and add or remove HTTP headers — without touching the origin application.