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Fastly Edge Function with JSON Response — Fastly-compute-edge Code

Returns a JSON response from a Fastly Edge function.

# fastly/demo/json.js
addEventListener('fetch', event => {
	event.respondWith(handleRequest(event.request))
})

async function handleRequest(request) {
	return new Response(JSON.stringify({ message: 'Hello, JSON!' }), {
		status: 200,
		headers: { 'Content-Type': 'application/json' }
	})
}

Fastly-compute-edge Language Guide

Fastly Compute@Edge is a high-performance, serverless edge computing platform that allows developers to deploy code closer to users, enabling low-latency web experiences and fast content delivery.

Primary Use Cases

  • ▸Dynamic content generation at the edge
  • ▸Real-time personalization for websites and apps
  • ▸Security enforcement (e.g., bot mitigation, access control)
  • ▸A/B testing and feature flagging without hitting origin
  • ▸API responses caching and optimization at edge nodes

Notable Features

  • ▸Serverless edge runtime with WebAssembly support
  • ▸Global deployment to Fastly edge locations
  • ▸Low-latency execution near users
  • ▸Integration with Fastly CDN and VCL
  • ▸Automatic scaling without server management

Origin & Creator

Compute@Edge was developed by Fastly, a company known for its edge cloud platform, and launched in 2019 to extend serverless capabilities to the edge.

Industrial Note

Compute@Edge is ideal for developers and enterprises needing ultra-low latency, edge-deployed serverless functions integrated with Fastly’s CDN for web acceleration and real-time traffic manipulation.

Quick Explain

  • ▸Compute@Edge lets you run custom code at Fastly's edge locations globally.
  • ▸Supports multiple languages and WebAssembly runtimes.
  • ▸Optimizes content delivery by reducing latency and offloading work from origin servers.
  • ▸Ideal for real-time personalization, security enforcement, and dynamic content generation.
  • ▸Provides deep integration with Fastly's CDN and caching infrastructure.

Core Features

  • ▸HTTP request/response handling at the edge
  • ▸Custom logic execution in Wasm runtimes
  • ▸Cache manipulation and content optimization
  • ▸Routing, redirects, and header transformations
  • ▸Logging and metrics collection for monitoring

Learning Path

  • ▸Learn WebAssembly basics
  • ▸Understand edge computing and CDN concepts
  • ▸Write and deploy a basic Compute@Edge function
  • ▸Integrate caching and routing logic
  • ▸Monitor performance and optimize edge delivery

Practical Examples

  • ▸Add custom security headers on all responses
  • ▸Personalize homepage content per user location
  • ▸Cache frequently requested API responses
  • ▸Redirect traffic based on device or geography
  • ▸Perform edge-based A/B testing for feature rollout

Comparisons

  • ▸Compute@Edge vs Google Cloud Functions: runs at edge nodes, lower latency, CDN integrated
  • ▸Compute@Edge vs AWS Lambda@Edge: similar edge serverless paradigm, Fastly emphasizes speed and developer ergonomics
  • ▸Compute@Edge vs FunctionX: FX is blockchain smart contracts, Compute@Edge is serverless CDN-edge compute
  • ▸Compute@Edge vs Cloudflare Workers: both edge compute, differences in platform, performance, and language support
  • ▸Compute@Edge vs traditional serverless: edge deployed, globally distributed vs centralized cloud functions

Strengths

  • ▸Ultra-low latency by running code at the edge
  • ▸Reduces origin server load
  • ▸High-performance, event-driven execution
  • ▸Tight integration with Fastly CDN
  • ▸Supports modern WebAssembly runtimes for multiple languages

Limitations

  • ▸Stateless by design; no persistent storage
  • ▸Limited execution duration and memory per request
  • ▸Requires understanding of edge computing concepts
  • ▸Debugging and local testing is less straightforward than cloud environments
  • ▸Vendor lock-in due to Fastly-specific platform features

When NOT to Use

  • ▸Long-running backend jobs
  • ▸Applications requiring persistent storage
  • ▸Heavy computational tasks exceeding Wasm limits
  • ▸Projects outside web/CDN delivery context
  • ▸Non-HTTP or non-CDN-driven workloads

Cheat Sheet

  • ▸fastly compute init - initialize project
  • ▸fastly compute build - compile WebAssembly module
  • ▸fastly compute deploy - deploy to edge
  • ▸fastly compute serve - local testing
  • ▸fastly compute logs - view edge logs

FAQ

  • ▸Is Compute@Edge free?
  • ▸Fastly offers free trial credits, then pay-per-use based on requests and bandwidth
  • ▸What languages are supported?
  • ▸Rust, AssemblyScript, C, and other WebAssembly-compatible languages
  • ▸Does it scale automatically?
  • ▸Yes - deployed globally at Fastly edge locations
  • ▸Can I access a database from edge?
  • ▸Yes, but latency may increase; best for caching or API aggregation
  • ▸How long can a function run?
  • ▸Execution limits depend on Fastly's Wasm runtime constraints, typically short-lived

30-Day Skill Plan

  • ▸Week 1: WebAssembly basics and Rust/AssemblyScript
  • ▸Week 2: Write simple HTTP transformations
  • ▸Week 3: Add caching and personalization logic
  • ▸Week 4: Integrate security headers and redirects
  • ▸Week 5: Optimize performance, logging, and multi-edge routing

Final Summary

  • ▸Fastly Compute@Edge is a serverless edge computing platform.
  • ▸Enables low-latency execution close to users via Fastly’s CDN.
  • ▸Supports WebAssembly runtimes for multiple languages.
  • ▸Ideal for personalization, caching, security, and dynamic content generation.
  • ▸Globally distributed, scalable, and integrated with Fastly’s edge services.

Project Structure

  • ▸src/ - source code for edge function
  • ▸Cargo.toml / package.json - project dependencies
  • ▸fastly.toml - Fastly service configuration
  • ▸dist/ - compiled WebAssembly modules
  • ▸scripts/ - build/deploy scripts

Monetization

  • ▸Accelerate high-traffic websites and apps
  • ▸Implement personalization and A/B testing
  • ▸Enhance security and compliance via edge rules
  • ▸Reduce origin server cost by caching at edge
  • ▸Optimize API response delivery for SaaS products

Productivity Tips

  • ▸Use Fastly CLI for rapid deployment
  • ▸Test locally before edge deployment
  • ▸Reuse WebAssembly modules for multiple services
  • ▸Monitor metrics for performance bottlenecks
  • ▸Automate deployments using CI/CD pipelines

Basic Concepts

  • ▸Edge Function - serverless code executed at edge nodes
  • ▸Service - collection of edge functions and configurations
  • ▸Version - versioned deployment of services
  • ▸Cache - content stored at edge for fast delivery
  • ▸Fastly VCL - domain-specific language for advanced routing and caching

Official Docs

  • ▸https://developer.fastly.com/learning/compute/
  • ▸https://developer.fastly.com/reference/compute/

More Fastly-compute-edge Typing Exercises

Simple Fastly Compute@Edge Function (JavaScript)Fastly Edge Function with Query ParametersFastly Edge Function with POST BodyFastly Edge Function with HeadersFastly Edge Function RedirectFastly Edge Function Error HandlingFastly Edge Function Delayed ResponseFastly Edge Function Fetch External APIFastly Edge Function Conditional Response

Practice Other Languages

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