Video lesson: Caching and Routing Change the Request Path

Lesson promise

By the end, the learner should be able to explain the core model for caching and routing change the request path, apply it to a concrete input, and identify when its usual shortcut or guarantee stops applying. This is a recording brief; publish it as a playable lesson after the narration and visual sequence have been produced and reviewed.

Narration draft

A cache stores reusable results near the request path to reduce repeated work or latency. Routing decides which server or shard handles a request. Together they affect freshness, locality, load distribution, and which layer is responsible for serving a particular version of data.

A cache-aside flow checks the cache, loads from the source on a miss, then stores the result with an expiry. A load balancer can distribute new connections among healthy backends, while consistent hashing can reduce key movement when a cache node changes.

Invalidation is difficult because writes and cache fills can race. Sticky routing may improve locality but make failover and uneven load harder. Cache keys must include every input that changes the result, especially tenant, locale, authorization, and version context.

Visual sequence

1. Put the input and assumptions on screen. Ask the learner to predict the next state before revealing it.
2. Animate the representation and show the operation one transition at a time.
3. Pause at the boundary case in the companion article and compare the result with the invariant.
4. End with the exercise prompt: A user updates a profile and immediately sees stale data from a cache. Compare expiry-only, explicit invalidation, and versioned cache keys for this consistency requirement.

Companion material

Use the article, trace, and interactive concept flow as the learner’s written and visual references. The video remains planned until an actual playable media URL and reviewed transcript are available.