Lua Scripts and Redis Functions

What you'll walk away with

Explain the core ideas behind Lua Scripts and Redis Functions
Run the sample Redis command or code and verify its output
Apply the technique correctly to the Tutorial Platform and production scenarios

Build the mental model

A Lua script runs multiple commands as one atomic server-side unit. Pass keys through KEYS and values through ARGV; declare every accessed key for cluster routing. Long scripts can block the server, so keep work bounded. Redis Functions package logic into named, persisted libraries.

Connect it to a real scenario

Implement a limited coupon claim that checks remaining stock, decrements it, and records the user in a claim set. Duplicate claims are no-ops and zero stock is rejected. On NOSCRIPT, load and retry, and record business outcome codes in metrics.

Keep atomic server-side logic short
Follow KEYS and ARGV conventions
Plan timeouts, return codes, and cluster keys

Try the working example

lua

if redis.call('SISMEMBER', KEYS[2], ARGV[1]) == 1 then return 2 end
local remaining = tonumber(redis.call('GET', KEYS[1]) or '0')
if remaining <= 0 then return 0 end
redis.call('DECR', KEYS[1])
redis.call('SADD', KEYS[2], ARGV[1])
return 1

-- KEYS: coupon:{42}:remaining, coupon:{42}:claims

You should see

The script atomically returns 0 for sold out, 1 for claimed, or 2 for duplicate.

5-minute try-it

Add success, blocked, and error outcome codes plus test cases to the rate-limit script.

One important caution

Do not run unbounded scans, loops, or external calls in Lua; the server event loop can be blocked.

Redis — Scripting with Lua — Redis

Easy traps

Do not run unbounded scans, loops, or external calls in Lua; the server event loop can be blocked.
Validate sample commands on a local or test instance with recoverable data before applying them to production Redis.

Exercise

Add success, blocked, and error outcome codes plus test cases to the rate-limit script.

You'll know it worked when: The script atomically returns 0 for sold out, 1 for claimed, or 2 for duplicate.