Throttling for rate limiting in Django - Step-by-Step Execution

Concept Flow - Throttling for rate limiting

Request Received

↓

Check Request Count

↓

Count < Limit?

No→Reject Request: 429 Too Many Requests

Yes↓

Process Request

↓

Update Request Count

↓

Send Response

When a request comes in, Django checks how many requests have been made recently. If the count is below the limit, it processes the request and updates the count. If not, it rejects the request to prevent overload.

Execution Sample

Django

from rest_framework.throttling import UserRateThrottle

class MyThrottle(UserRateThrottle):
    rate = '3/min'

# In view
throttle_classes = [MyThrottle]

This code limits each user to 3 requests per minute using Django REST Framework's throttling.

Execution Table

Step	Request Number	Request Count	Condition (Count < 3)	Action	Response
1	1	0	True	Process request, increment count to 1	200 OK
2	2	1	True	Process request, increment count to 2	200 OK
3	3	2	True	Process request, increment count to 3	200 OK
4	4	3	False	Reject request	429 Too Many Requests

💡 At step 4, request count reaches limit 3, so condition fails and request is rejected.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4 (Rejected)
request_count	0	1	2	3	3
response_status	None	200 OK	200 OK	200 OK	429 Too Many Requests

Key Moments - 2 Insights

Why is the 4th request rejected even though it is close to the limit?

Because the limit is 3 requests per minute, once the count reaches 3 (see step 3 in execution_table), the next request (step 4) fails the condition and is rejected.

Does the request count reset automatically?

Yes, the count resets after the time window (1 minute here). This is managed internally by the throttle class, so after 1 minute, requests can be accepted again.

Visual Quiz - 3 Questions

Look at the execution table, what is the response status at step 3?

A 429 Too Many Requests

B 500 Internal Server Error

C 200 OK

D 404 Not Found

💡 Hint

Check the 'Response' column at step 3 in the execution_table.

At which step does the request count reach the limit?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Request Count' and 'Condition' columns in execution_table.

If the rate was changed to '5/min', what would happen at step 4?

A Request would be processed with 200 OK

B Request would be rejected with 429

C Request count would reset

D Server would crash

💡 Hint

Think about the limit and compare with the request count at step 4.

Concept Snapshot

Throttling limits how many requests a user can make in a time window.
In Django REST Framework, create a throttle class with a rate like '3/min'.
Each request checks if count < limit; if yes, process and increment count.
If count reaches limit, reject with 429 Too Many Requests.
Counts reset after the time window automatically.

Full Transcript

Throttling in Django REST Framework helps control how many requests a user can make in a set time. When a request arrives, the system checks how many requests the user has made recently. If the user is under the limit, the request is processed and the count increases. If the user hits the limit, the request is rejected with a 429 error. The count resets after the time window, allowing new requests. This prevents server overload and keeps the app responsive.

Practice

1. What is the main purpose of throttling in Django REST Framework?

easy

A. To cache API responses for faster access

B. To limit the number of requests a user can make in a given time period

C. To authenticate users before accessing the API

D. To speed up the response time of the server

Solution

1. Step 1: Understand throttling concept

   Throttling is designed to control how many requests a user can send to the server in a set time.

2. Step 2: Identify purpose in Django REST Framework

   It prevents abuse by limiting request rates, not speeding responses or authentication.

3. Final Answer:

   To limit the number of requests a user can make in a given time period -> Option B

4. Quick Check:

   Throttling = request limit [OK]

Hint: Throttling controls request counts per time [OK]

Common Mistakes:

• Confusing throttling with authentication
• Thinking throttling speeds up responses
• Mixing throttling with caching

2. Which of the following is the correct way to set a throttle rate of 10 requests per minute in a custom throttle class?

easy

A. rate = '10/minute'

B. rate = '10/second'

C. rate = 'minute/10'

D. rate = '10 requests per minute'

Solution

1. Step 1: Recall throttle rate format

   The rate must be a string with number and time unit separated by a slash, e.g., '10/minute'.

2. Step 2: Match correct syntax

   Only '10/minute' matches the required format; others are invalid or incorrect syntax.

3. Final Answer:

   rate = '10/minute' -> Option A

4. Quick Check:

   Throttle rate format = 'number/time' [OK]

Hint: Throttle rate uses 'number/time' string format [OK]

Common Mistakes:

• Using spaces or words instead of slash format
• Swapping number and time units
• Using unsupported time units

3. Given this view with throttling applied:

from rest_framework.throttling import UserRateThrottle

class MyThrottle(UserRateThrottle):
    rate = '3/minute'

class MyView(APIView):
    throttle_classes = [MyThrottle]

    def get(self, request):
        return Response({'message': 'Hello'})

What happens if a user makes 4 GET requests within one minute?

medium

A. The 4th request is delayed but eventually succeeds

B. All 4 requests succeed with status 200

C. The 4th request is blocked with a 429 Too Many Requests error

D. The server crashes due to too many requests

Solution

1. Step 1: Understand throttle rate and behavior

   The throttle allows 3 requests per minute per user; the 4th exceeds the limit.

2. Step 2: Identify response to exceeding limit

   When limit is exceeded, Django REST Framework returns HTTP 429 error blocking the request.

3. Final Answer:

   The 4th request is blocked with a 429 Too Many Requests error -> Option C

4. Quick Check:

   Requests > rate limit = 429 error [OK]

Hint: Requests over limit get 429 error [OK]

Common Mistakes:

• Assuming all requests succeed
• Thinking requests get delayed instead of blocked
• Believing server crashes on too many requests

4. Identify the error in this custom throttle class:

from rest_framework.throttling import SimpleRateThrottle

class CustomThrottle(SimpleRateThrottle):
    scope = 'custom'

    def get_cache_key(self, request, view):
        return request.user.id

# settings.py
REST_FRAMEWORK = {
    'DEFAULT_THROTTLE_RATES': {
        'custom': '5/minute'
    }
}

medium

A. get_cache_key should return a string, but returns an integer

B. scope should be set to 'rate' instead of 'custom'

C. DEFAULT_THROTTLE_RATES key 'custom' is missing a time unit

D. CustomThrottle must inherit from UserRateThrottle, not SimpleRateThrottle

Solution

1. Step 1: Check get_cache_key return type

   The method returns request.user.id, which is an integer, but cache keys must be strings.

2. Step 2: Validate other parts

   Scope 'custom' matches the throttle rate key, and inheritance from SimpleRateThrottle is valid.

3. Final Answer:

   get_cache_key should return a string, but returns an integer -> Option A

4. Quick Check:

   Cache key must be string [OK]

Hint: Cache keys must be strings, not integers [OK]

Common Mistakes:

• Returning non-string cache keys
• Misnaming throttle scope
• Confusing throttle class inheritance

5. You want to apply different throttle rates for authenticated and anonymous users in Django REST Framework. Which approach correctly implements this?

hard

A. Set a single throttle class with rate '10/minute' and check user status inside get_cache_key

B. Use middleware to block anonymous users after 5 requests per minute instead of throttling classes

C. Apply throttling only to authenticated users by setting throttle_classes conditionally in the view

D. Use two throttle classes: one with 'user' scope for authenticated, one with 'anon' scope for anonymous, and add both to the view's throttle_classes

Solution

1. Step 1: Understand throttling for different user types

   Django REST Framework supports multiple throttle classes to handle different user types separately.

2. Step 2: Apply correct method

   Using two throttle classes with 'user' and 'anon' scopes and adding both to throttle_classes is the standard way.

3. Final Answer:

   Use two throttle classes: one with 'user' scope for authenticated, one with 'anon' scope for anonymous, and add both to the view's throttle_classes -> Option D

4. Quick Check:

   Multiple throttle classes handle user types separately [OK]

Hint: Use separate throttle classes for user and anon [OK]

Common Mistakes:

• Trying to handle both user types in one throttle class
• Using middleware instead of throttle classes
• Conditionally setting throttle_classes in the view