Design fencing tokens for locks

Prompt that designs fencing tokens for distributed locks and prevents split-brain after expiry. Paste it into an AI tool of your choice, which then designs fencing tokens for locks.

Topic: Apps & prototypes
Type: Prompt
Level: Intermediate
Time: about 15 min

Results depend on the tool, the model and what you enter.

Result preview

Example: written by our editors, not real AI output.

Resource: order-queue Lock: Redis SET NX PX 30000 Problem: holder expired, still writing Token: monotonic int in storage Write only if token >= stored Reject: 409 + re-acquire Test: old holder after TTL, new holder wins

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ResourceWhat is protected?

LockPattern today?

RiskWhat already happened?

Your prompt

Help me design a fencing token for a distributed lock.
Resource: [Resource]
Lock: [Lock]
Risk: [Risk]
Steps: 1. Read who writes the resource and how the lock is granted and renewed today. 2. Explain why TTL alone does not stop split-brain when the old holder still writes. 3. Propose a monotonically rising token that storage checks on every write. 4. Define what happens on a rejected token and how clients re-acquire. 5. Separate lock TTL, heartbeat and fencing clearly. 6. Write tests for an expired holder and double writers.
Output: token rule, storage check, rejection behaviour and test cases.

Take particular care to check every write against a rising token, not only against TTL.

Before you answer, check: Are all instructions met? If key information is missing or a placeholder in square brackets is still in the text, ask instead of guessing. Mark assumptions as assumptions.

This is an instruction for an AI, not the result itself.

Where this prompt works

These AI tools are a good fit for this prompt:

How to use it

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Copy the finished prompt into an AI tool of your choice.
Paste lock code, TTL and an example of competing writers, without production secrets.

Why does this work?

A lock expires and the old worker still writes. Without fencing, storage accepts both. With a token, only the higher number wins.

Tips

Store the token next to the value and hard-reject smaller numbers.

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Design fencing tokens for locks

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