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CAP Theorem Interactive Explorer

Run the CAP Theorem Explorer MicroSim Fullscreen
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About This MicroSim

This MicroSim makes the CAP theorem concrete. Two database replicas (Node A and Node B) are joined by a network link. You choose CP (consistency) or AP (availability) mode, write to A, read from B, and create or heal a network partition. Under a partition, the difference becomes visible: a CP system rejects reads from B to avoid returning stale data, while an AP system serves a possibly stale value and converges once the partition heals. Three scenario presets show when each model is the right choice.

How to Use

  1. Pick CP or AP with the mode switch.
  2. Send Write → A and Read ← B while the network is healthy — everything is consistent.
  3. Create Partition, then write to A and read from B again. In CP the read is rejected; in AP it returns a stale value with a warning.
  4. Heal Partition in AP mode to watch Node B converge to Node A (eventual consistency).
  5. Load a scenario (Financial ledger, Shopping cart, Profile update) to see which model fits and why; use Explain for the rationale.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

<iframe src="https://dmccreary.github.io/atam/sims/cap-theorem-explorer/main.html"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Grade Level

Undergraduate / Professional

Duration

15-20 minutes

Prerequisites

Familiarity with replication and the CAP theorem (consistency, availability, partition tolerance).

Bloom's Taxonomy Level

Apply (L3)

Learning Objective

Students will be able to predict the behavior of CP and AP database systems under a network partition and select the appropriate consistency model given the quality attribute priorities of a specific scenario.

Activities

  1. Predict (6 min): Before reading from B under a partition, students predict the result in CP and in AP, then verify.
  2. Convergence (5 min): Students observe AP convergence after healing and explain "eventual consistency" in their own words.
  3. Choose (6 min): For each preset scenario, students justify the recommended model from the quality attribute priorities.

Assessment

Give students three new scenarios and ask them to choose CP or AP and justify the choice from the partition behavior.

References

  1. Bass, L., Clements, P., & Kazman, R. (2021). Software Architecture in Practice (4th ed.). Addison-Wesley.
  2. Kleppmann, M. (2017). Designing Data-Intensive Applications. O'Reilly. (Consistency and the CAP theorem.)