Rate limiting with sliding window in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add the current timestamp to the sorted set for rate limiting.

Redis

redis.call('ZADD', 'user:[1]:requests', current_time, current_time)

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A123

Blimit

Ctimestamp

Duser123

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic word like 'timestamp' instead of a user ID.

Using 'user123' which results in malformed key 'user:user123:requests'.

The key for the sorted set should uniquely identify the user, such as '123'.

2fill in blank

medium

Complete the code to remove timestamps older than the sliding window duration.

Redis

redis.call('ZREMRANGEBYSCORE', 'user:123:requests', 0, current_time [1] window_size)

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A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of subtraction.

Using multiplication or division which are incorrect here.

We subtract the window size from the current time to remove old timestamps.

3fill in blank

hard

Fix the error in the code to count requests within the sliding window.

Redis

local count = redis.call('ZCOUNT', 'user:123:requests', current_time [1] window_size, current_time)

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A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of subtraction in the range.

Using multiplication or division which are invalid here.

We count timestamps from current_time - window_size up to current_time.

4fill in blank

hard

Fill both blanks to complete the Lua script that enforces rate limiting with sliding window.

Redis

if count [1] limit then
  return [2]
end

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A>=

Btrue

C<=

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' instead of '>=' for the condition.

Returning true to block the request instead of false.

If the count is greater than or equal to the limit, return false to block the request.

5fill in blank

hard

Fill all three blanks to complete the Lua script that adds the request timestamp, cleans old entries, and returns true if allowed.

Redis

redis.call('ZREMRANGEBYSCORE', 'user:123:requests', 0, current_time [1] window_size)
local count = redis.call('ZCOUNT', 'user:123:requests', current_time [2] window_size, current_time)
if count [3] limit then
  return false
end
redis.call('ZADD', 'user:123:requests', current_time, current_time)
return true

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

A-

B+

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition instead of subtraction for score ranges.

Using '<=' instead of '>=' in the if condition.

We subtract window_size to remove old timestamps and count requests in the sliding window. If count is greater or equal to limit, block the request.