What is Edge Computing and How Do Isolates, WebAssembly (WASM), and Container Models Compare?

Edge computing extends CDNs from simple caching into programmable data planes where lightweight functions or containers execute on the request path at PoPs. Instead of merely serving cached bytes, edge compute personalizes, filters, transforms, or routes traffic without round trips to centralized regions. This architecture reduces end to end latency for dynamic logic and decreases backbone transit costs. The execution model is typically event driven and stateless. When state is required, it comes from edge key value stores or short lived caches rather than cross region database calls that would add 50+ ms latency. Providers offer different runtime models with distinct trade offs. JavaScript isolates and WebAssembly (WASM) provide the fastest execution, routinely achieving sub millisecond processing for simple logic like header rewrites, redirects, and token validation. These runtimes target execution budgets under 50 milliseconds (ms) CPU time per invocation and impose strict code size limits (typically a few megabytes). Isolates achieve this speed by running within a shared virtual machine process with strong isolation between tenants, avoiding the overhead of full process or virtual machine boundaries. However, they offer limited standard libraries and constrain language choices. Container based edge compute supports richer dependencies and fuller language ecosystems but incurs cold start penalties when containers must initialize. Cold starts can add hundreds of milliseconds of unpredictable latency, making containers better suited for non latency critical paths or scenarios where pre warming is feasible. Production deployments must account for strict resource constraints. Edge functions typically have CPU time limits (50 ms per request is common), memory caps (128 to 512 megabytes), and execution timeouts. Exceeding these limits causes aborted executions and tail latency spikes. Multi tenant isolate and WASM runtimes also face residual security risks from side channel attacks like Spectre and Meltdown variants, though providers continually harden runtimes. Despite constraints, edge compute excels for use cases like authorization checks, A/B test bucketing, personalized redirects, URL rewrites for image optimization, and stateless data enrichment where the logic is deterministic and lightweight.

Amazon CloudFront Functions run ultra lightweight JavaScript at edge with sub millisecond execution targets for tasks like adding security headers, normalizing URLs, and performing simple redirects. For heavier logic like JWT validation or API composition, Lambda@Edge uses full Lambda containers but accepts cold start trade offs.

Adobe Experience Platform (AEP) Edge Network pushes personalization logic to the edge, caching user segments and context near users. Stateless enrichment and routing run in real time at PoPs, treating dynamic per user data like a CDN treats static bytes, enabling sub 50 ms personalization decisions.

An e-commerce site uses edge compute to rewrite image URLs based on User Agent, serving WebP to supporting browsers and JPEG to others. This logic runs in under 5 ms at edge rather than adding a 100 ms round trip to central image processing services.