Edge Computing & Edge Functions Flashcards

What is the role of the Cache-Tag (or surrogate key) header in edge computing deployments?

Answer: It associates cached responses with logical tags so they can be purged in bulk with a single API call

Cache-Tag / surrogate key headers let operators invalidate groups of related cached objects atomically without knowing exact URLs.

Which of the following correctly describes the execution environment difference between Cloudflare Workers and AWS Lambda@Edge?

Answer: Workers run in V8 Isolates with sub-millisecond cold starts; Lambda@Edge runs in full Node.js containers with higher cold-start latency

Cloudflare Workers use lightweight V8 Isolates for near-zero cold starts, while Lambda@Edge runs in managed containers with higher initialization overhead.

What does 'fan-out' mean in the context of edge function subrequests?

Answer: An edge function making multiple parallel upstream requests to assemble a composite response

Fan-out allows an edge function to fetch data from several microservices or APIs concurrently, then merge the results into one response for the client.

A streaming edge function uses the TransformStream API. What is the main benefit over a buffered response approach?

Answer: It reduces Time To First Byte by piping response chunks to the client as they arrive rather than waiting for the full response

Streaming responses let the edge begin forwarding data to the client immediately, improving perceived performance for large or slow-generating payloads.

What is 'stale-while-revalidate' (SWR) and what problem does it solve at the edge?

Answer: A caching directive that serves a stale cached response immediately while refreshing the cache in the background, eliminating latency spikes on cache expiry

SWR decouples cache freshness from user-facing latency so users always get a fast cached hit while the edge silently updates the entry for the next request.

Which edge function event hook allows you to modify an HTTP response before it is delivered to the client, including adding security headers?

Answer: The response transform phase within event.respondWith() after fetching from origin

Platforms expose a response-phase hook (within event.respondWith()) where developers can mutate the Response object to inject security headers like CSP or HSTS.

Why is the edge function bundle size important, and what is a common size limit imposed by CDN platforms?

Answer: Bundle size affects cold-start time and memory usage; platforms often cap bundles at 1 to 10 MB (e.g., Cloudflare Workers at 10 MB compressed)

Oversized bundles increase isolate initialization time and memory footprint, so platforms impose strict size caps to maintain the low-latency guarantees of edge execution.