These Algo. typically used as Rate limiting Algorithm.
It is used to control amount of data or number of requests that can be proccessed in a given time period.
WORKING :
- Token are added to the Bucket at a fixed rate.
- The Bucket has a Max. Capacity, it can't hold more tokens than that.
- When a Request came, the Bucket is checked for number of token available
- If req. tokens are available then remove that tokens from the bucket and process the request.
- If no token are available, the request is rejected or pushed to a retry queue.
IMPLEMENTATION :
Token Bucket can be implemented in respect to user or application.
Means either we can use it rate limit the user, that a certain user can only make 10req/sec.
or we can use it to rate limit the application, that a certain application can only make 10req/sec.
class TokenBucket{ private refillRate:number; // no of token added to the bucket per second private capacity:number; private Bucket: number; private lastRefillTime: number; constructor(refillRate:number,capacity:number){ this.refillRate = refillRate; this.capacity = capacity; this.Bucket = capacity; this.lastRefillTime = Date.now(); } public refill(){ const time = Date.now(); const diff = time - this.lastRefillTime; const tokensToAdd = Math.floor(diff* this.refillRate); this.Bucket = min(this.capacity, this.Bucket+tokensToAdd); this.lastRefillTime = time; } public allowRequest(){ // Update the Bucket with tokens refill(); if(this.Bucket >= 1){ this.Bucket = this.Bucket - 1; return true; } return false; } } Example : LIMITING REQUESTS PER SECOND FOR USER IN NESTJS
FLOW
Client ──> NestJS API (Producer) └── always send to RabbitMQ ➤ (free or premium queue) Worker (Consumer) └── Pull from queue(s) └── Check Redis token bucket ├── ✅ Allowed → process job └── ⛔ Not allowed → requeue with delay 
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