Rate Limiting: The Unsung Hero of Web Development

What is Rate Limiting?

Rate limiting is the process of controlling how many requests your application users can make within a specified time frame. This is necessary for several reasons:

• Ensuring your application functions regardless of incoming traffic
• Implementing usage limits for certain users or features
• Protecting your application from Denial of Service (DoS) and other cyber attacks

Rate Limiting Algorithms

There are several algorithms used in rate limiting, each with its unique advantages and disadvantages:

• Token Bucket Algorithm: Tokens are added to a bucket at a fixed rate, and each request consumes a token. When the bucket is empty, new requests are rejected.
• Leaky Bucket Algorithm: Requests are added to a bucket, and removed at a fixed rate. If the bucket fills up, additional requests are rejected or delayed.
• Fixed Window Algorithm: Tracks the number of requests made within a fixed time window. If the limit is exceeded, requests are rejected or delayed until the next window.
• Sliding Window Algorithm: Similar to the fixed window algorithm, but the window size is fixed, and the start of the window is determined by the user’s first request.

Implementing Rate Limiting in Go Applications

To implement rate limiting in Go applications, we’ll use the x/time/rate package, which provides a simple and efficient way to limit the number of requests.

Step 1: Create a Limiter

limiter := rate.NewLimiter(rate.Every(1*time.Second), 5)

Step 2: Use the Limiter

if!limiter.Allow() {
    http.Error(w, "Rate limit exceeded", http.StatusTooManyRequests)
    return
}

Per-Client Rate Limiting

To implement per-client rate limiting, we’ll use a map to store the limiter for each client. We’ll also use a mutex to protect the map from concurrent access.

var clients = make(map[string]*rate.Limiter)
var mu sync.Mutex

func getLimiter(ip string) rate.Limiter {
    mu.Lock()
    defer mu.Unlock()
    limiter, ok := clients[ip]
    if!ok {
        limiter = rate.NewLimiter(rate.Every(1*time.Second), 5)
        clients[ip] = limiter
    }
    return limiter
}

Rate Limiting with Tollbooth

Tollbooth is a Go package that provides a simple and efficient way to implement rate limiting. It uses the token bucket algorithm and provides a clean and simple API.

import (
    "github.com/didip/tollbooth"
    "github.com/didip/tollbooth/limiter"
)

func main() {
    // Create a limiter
    limiter := tollbooth.NewLimiter(1*time.Second, 5)

    // Use the limiter
    if!limiter.Allow() {
        http.Error(w, "Rate limit exceeded", http.StatusTooManyRequests)
        return
    }
}