Cache and origin design: choose freshness, variation and failure behavior together

Proposed flow for this scenario

1. 1Classify response and authorization
2. 2Choose safe variation key
3. 3Apply freshness policy
4. 4Serve suitable hit or retrieve origin
5. 5Handle failure and update
6. 6Verify customer-visible revision

This flow describes a design to evaluate. The local experiment explores one stated mechanism. Its scope appears with the controls; the proposed services are not provisioned.

Decision checkpoints

Start with who may receive the same response

QuantumSketch’s public illustration scene-v2.svg can be identical for every viewer. LetX job status may vary by customer identity, job ownership and update time. A cache policy appropriate for the first does not become safe for the second just because both responses are HTTP.

List every input that can change the representation and every access requirement. Decide whether those variations belong in a safe cache key, require another approach or should bypass shared caching. Do not improve a hit-rate number by removing a field that separates customer responses.

The cache key is a correctness decision

Real CloudFront cache policies control selected request variation in the cache key. Forwarding information to an origin and including it in the cache key are different responsibilities. If the origin uses a value to vary a cacheable response, review how that variation is represented.

More variation can lower the hit rate, but less variation can return the wrong content. Test two deliberately different request contexts and inspect whether the intended representations remain separate. The local console has a path-only cache and cannot validate query, cookie, header or authenticated-customer variants.

Freshness and failure need explicit answers

Choose the longest stale interval that the response’s business meaning permits, then review the real cache policy and origin header interaction. A public illustration can tolerate different rules from a job completion status or an access-revoked document.

Decide what happens when the origin is unavailable, when it returns an error and when content is revoked. Avoid relying on an unspecified stale response as an outage plan. The local CloudFront exercise does not model Cache-Control precedence, cached errors, stale directives or production origin retry behavior.

Separate routine releases from emergency correction

Use a new filename for an immutable public asset release and retain dependencies required by older HTML or rollback. For an existing URL requiring a quicker correction, identify the proper invalidation path and verify the origin content before requesting a fresh fetch.

The private-S3 architecture guide explains origin access and HTTPS prerequisites; this page addresses cache correctness and economics. An OAC controls the origin request, but does not by itself choose a safe cache key or authorize every viewer. Origin privacy and response-sharing safety remain separate design questions.

Keep a representation worksheet alongside the cache policy: requested path, customer context, expected revision, authorization requirement and acceptable age. Compare two request contexts that should differ and two that should share a response. This makes accidental sharing visible before a production hit-rate graph encourages broader caching than the product can safely permit.

Use the model, then change the requirement

In the local CloudFront console, request a synthetic path, replace the origin body and compare a hit with an expired or invalidated miss. In the cost experiment below, vary hypothetical hit rate and fixed cache cost. Neither exercise measures real edge latency or calculates AWS billing.

Question: LetX adds customer-specific status text to a formerly public cacheable path. Is keeping the same long path-only cache safe? No. Revisit viewer authorization, response variation, freshness and revocation before serving the new representation. The resulting design may deliberately sacrifice shared hits to preserve correctness.

Practice the supported console workflow

• Inspect selected cache hits and origin decisions

  Uses simulated resources stored on this device. No website account or AWS credentials required.

  Explore ↗

• Inspect source object revisions

  Uses simulated resources stored on this device. No website account or AWS credentials required.

  Explore ↗

Sources and scope

Reviewed against these official references. The model’s supported scope appears alongside its controls.

• AWS: cache-key policy responsibilities
• AWS: expiration and origin-header interaction
• AWS: invalidation versus versioned filenames