Rate limiter with INCR and EXPIRE in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to increment the request count for a user key.

Redis

redis.call('INCR', [1])

Drag options to blanks, or click blank then click option'

Auser_key

Bexpire_time

Climit

Dtimestamp

Attempts:

3 left

💡 Hint

Common Mistakes

Using expire_time instead of the key to increment

Using limit which is a number, not a key

The INCR command increments the count for the given user key.

2fill in blank

medium

Complete the code to set the expiration time for the user key.

Redis

redis.call('EXPIRE', [1], 60)

Drag options to blanks, or click blank then click option'

Acount

Btimestamp

Cuser_key

Dlimit

Attempts:

3 left

💡 Hint

Common Mistakes

Setting expiration on a number or limit instead of the key

Using wrong key name

The EXPIRE command sets the expiration time on the user key to 60 seconds.

3fill in blank

hard

Fix the error in the code to check if the key exists before setting expiration.

Redis

if redis.call('EXISTS', [1]) == 1 then redis.call('EXPIRE', [1], 60) end

Drag options to blanks, or click blank then click option'

Alimit

Buser_key

Ccount

Dtimestamp

Attempts:

3 left

💡 Hint

Common Mistakes

Checking existence of wrong key

Using count or limit instead of key

We check if the user_key exists before setting expiration on it.

4fill in blank

hard

Fill both blanks to create a Lua script that increments the user key and sets expiration if it's a new key.

Redis

local current = redis.call('INCR', [1])
if current == 1 then redis.call('EXPIRE', [2], 60) end
return current

Drag options to blanks, or click blank then click option'

Auser_key

Blimit

Dtimestamp

Attempts:

3 left

💡 Hint

Common Mistakes

Using different keys for increment and expire

Using limit or timestamp instead of user_key

The script increments the user_key and sets expiration on the same key if it's the first increment.

5fill in blank

hard

Fill all three blanks to complete the Lua script that increments the user key, sets expiration, and checks if the limit is exceeded.

Redis

local current = redis.call('INCR', [1])
if current == 1 then redis.call('EXPIRE', [2], 60) end
if current > [3] then return 0 else return 1 end

Drag options to blanks, or click blank then click option'

Auser_key

Climit

Dtimestamp

Attempts:

3 left

💡 Hint

Common Mistakes

Using timestamp instead of user_key for increment

Mixing keys and limit values

Not comparing count to limit

The script increments the user_key, sets expiration on it, and compares the count to the limit to decide if the request is allowed.