Rate Limiting

Sentinel provides multi-dimensional rate limiting with sliding window counters. You can enforce limits per IP address, per authenticated user, per route, and globally — all at the same time. Every dimension is evaluated independently, and a request must pass all applicable limits to be allowed through.

Enabling Rate Limiting

The simplest way to get started is to enable rate limiting with a single per-IP limit. This protects every route in your application from individual clients sending too many requests.

1import (
2    "time"
3
4    sentinel "github.com/MUKE-coder/sentinel"
5    "github.com/gin-gonic/gin"
6)
7
8func main() {
9    r := gin.Default()
10
11    sentinel.Mount(r, nil, sentinel.Config{
12        RateLimit: sentinel.RateLimitConfig{
13            Enabled: true,
14            ByIP:    &sentinel.Limit{Requests: 100, Window: time.Minute},
15        },
16    })
17
18    r.GET("/api/hello", func(c *gin.Context) {
19        c.JSON(200, gin.H{"message": "Hello, World!"})
20    })
21
22    r.Run(":8080")
23}

Rate Limit Dimensions

Sentinel supports four independent rate limit dimensions. You can use any combination of them. Each dimension maintains its own set of counters and is evaluated in a specific order.

The Limit Struct

Every dimension is configured with the same Limit struct, which defines a maximum number of requests within a time window.

type Limit struct {
    Requests int           // Maximum requests allowed within the window
    Window   time.Duration // Time window (e.g., time.Minute, 15 * time.Minute)
}

Per-IP (ByIP)

Each unique client IP address gets its own counter. This is the most common dimension and protects against individual clients overwhelming your server.

// 100 requests per minute per IP address
ByIP: &sentinel.Limit{Requests: 100, Window: time.Minute}

Per-User (ByUser)

Each authenticated user gets their own counter, identified by a user ID string. This requires a UserIDExtractor function that extracts the user ID from the request. If the extractor returns an empty string (unauthenticated request), the per-user limit is skipped for that request.

// 500 requests per minute per authenticated user
ByUser: &sentinel.Limit{Requests: 500, Window: time.Minute},

// Tell Sentinel how to identify the user
UserIDExtractor: func(c *gin.Context) string {
    return c.GetHeader("X-User-ID")
},

Per-Route (ByRoute)

Different routes can have different limits. The ByRoute map keys are exact route paths. Each route limit is tracked per IP address (the counter key is a combination of the route path and the client IP).

// Strict limits on sensitive endpoints
ByRoute: map[string]sentinel.Limit{
    "/api/login":          {Requests: 5, Window: 15 * time.Minute},
    "/api/register":       {Requests: 3, Window: time.Hour},
    "/api/password-reset": {Requests: 3, Window: time.Hour},
},

Global

A single counter shared across all requests regardless of source. This is a safety net to protect your application from being overwhelmed by aggregate traffic.

// 5000 total requests per minute across all clients
Global: &sentinel.Limit{Requests: 5000, Window: time.Minute}

All Dimensions Together

1RateLimit: sentinel.RateLimitConfig{
2    Enabled:  true,
3    Strategy: sentinel.SlidingWindow,
4
5    // Per-IP: 100 req/min
6    ByIP: &sentinel.Limit{Requests: 100, Window: time.Minute},
7
8    // Per-user: 500 req/min (requires UserIDExtractor)
9    ByUser: &sentinel.Limit{Requests: 500, Window: time.Minute},
10
11    // Per-route: different limits for sensitive endpoints
12    ByRoute: map[string]sentinel.Limit{
13        "/api/login":    {Requests: 5, Window: 15 * time.Minute},
14        "/api/register": {Requests: 3, Window: time.Hour},
15    },
16
17    // Global: 5000 req/min total
18    Global: &sentinel.Limit{Requests: 5000, Window: time.Minute},
19
20    // Extract user ID for per-user limiting
21    UserIDExtractor: func(c *gin.Context) string {
22        return c.GetHeader("X-User-ID")
23    },
24}

Configuration Reference

Priority Order

When multiple dimensions are configured, Sentinel evaluates them in a specific order. The request is rejected as soon as any dimension's limit is exceeded — remaining dimensions are not checked.

Response Headers

Sentinel automatically sets standard rate limit headers on responses so clients can self-regulate. When a limit is exceeded, the client receives a 429 Too Many Requests response with a JSON body.

On a successful request, the response includes X-RateLimit-Limit and X-RateLimit-Remaining based on the per-IP limit. When a limit is exceeded, the response body is:

{
    "error": "Rate limit exceeded",
    "code": "RATE_LIMITED"
}

Per-Route Limits

Per-route limits let you apply different thresholds to different endpoints. This is especially useful for protecting sensitive routes like login, registration, and password reset endpoints with much stricter limits than the rest of your API.

1sentinel.Mount(r, nil, sentinel.Config{
2    RateLimit: sentinel.RateLimitConfig{
3        Enabled: true,
4
5        // General API limit: 100 req/min per IP
6        ByIP: &sentinel.Limit{Requests: 100, Window: time.Minute},
7
8        // Strict limits on sensitive routes
9        ByRoute: map[string]sentinel.Limit{
10            // Login: 5 attempts per 15 minutes per IP
11            "/api/login": {Requests: 5, Window: 15 * time.Minute},
12
13            // Registration: 3 per hour per IP
14            "/api/register": {Requests: 3, Window: time.Hour},
15
16            // Password reset: 3 per hour per IP
17            "/api/password-reset": {Requests: 3, Window: time.Hour},
18
19            // File upload: 10 per minute per IP
20            "/api/upload": {Requests: 10, Window: time.Minute},
21        },
22    },
23})

Route limits are keyed by the combination of the route path and the client IP. For example, a request to /api/login from IP 1.2.3.4 uses the counter key route:/api/login:1.2.3.4. This means each IP gets its own counter for each route-limited path.

How It Works

Sentinel uses sliding window counters stored entirely in memory. Each counter tracks a request count and a window expiration timestamp.

1. When a request arrives, Sentinel looks up the counter for the relevant key (e.g., ip:1.2.3.4).
2. If no counter exists, or the current time is past the window expiration, a new counter is created with a count of 1 and a window end of now + Window.
3. If the counter exists and the window has not expired, the count is incremented.
4. If the count exceeds the configured limit, the request is rejected with a 429 status.

A background goroutine runs every 30 seconds to clean up expired counters, preventing unbounded memory growth. The cleanup removes any counter whose window has passed.

// Internal counter structure (simplified)
type rateLimitEntry struct {
    count     int       // Number of requests in the current window
    windowEnd time.Time // When the current window expires
}

// Cleanup runs every 30 seconds, removing expired entries
func (rl *RateLimiter) cleanup() {
    ticker := time.NewTicker(30 * time.Second)
    for range ticker.C {
        now := time.Now()
        for key, entry := range rl.counters {
            if now.After(entry.windowEnd) {
                delete(rl.counters, key)
            }
        }
    }
}

Dashboard Management

The Sentinel dashboard includes a dedicated Rate Limits page that gives you real-time visibility into your rate limit counters and configuration.

Live Counter States

The dashboard displays all active rate limit counters in real time. Each entry shows the counter key, the current request count, the window expiration time, and how many requests remain. Counters are automatically removed from the view when their window expires.

Edit Per-Route Limits

You can edit per-route limits directly from the dashboard without restarting your application. This is useful for responding to traffic spikes or adjusting thresholds after observing real-world patterns.

Reset Individual Counters

If a legitimate client gets rate-limited (e.g., during testing or after a deployment), you can reset their counter from the dashboard. This removes the specific counter key, allowing the client to send requests again immediately.

Testing

You can verify rate limiting is working by sending rapid requests with curl and inspecting the response headers.

Check Rate Limit Headers

# Send a request and inspect rate limit headers
curl -v http://localhost:8080/api/hello 2>&1 | grep -i "x-ratelimit\|retry-after"

# Expected output (first request):
# < X-RateLimit-Limit: 100
# < X-RateLimit-Remaining: 99

Hit the Rate Limit

# Send requests in a tight loop to trigger the limit
# (adjust the count based on your configured limit)
for i in $(seq 1 110); do
    STATUS=$(curl -s -o /dev/null -w "%{http_code}" http://localhost:8080/api/hello)
    echo "Request $i: HTTP $STATUS"
done

# You should see HTTP 200 for the first 100 requests,
# then HTTP 429 once the limit is exceeded.

Test Per-Route Limits

# Test the login endpoint (5 requests per 15 minutes)
for i in $(seq 1 7); do
    RESPONSE=$(curl -s -w "\nHTTP %{http_code}" \
        -X POST http://localhost:8080/api/login \
        -H "Content-Type: application/json" \
        -d '{"email":"test@example.com","password":"test"}')
    echo "Request $i: $RESPONSE"
done

# Requests 1-5: normal response
# Requests 6-7: HTTP 429 with Retry-After header

Inspect a 429 Response

# After exceeding the limit, inspect the full 429 response
curl -v http://localhost:8080/api/hello 2>&1

# Response headers will include:
# < HTTP/1.1 429 Too Many Requests
# < X-RateLimit-Limit: 100
# < X-RateLimit-Remaining: 0
# < Retry-After: 60
#
# Response body:
# {"code":"RATE_LIMITED","error":"Rate limit exceeded"}

Limitations

The current rate limiter implementation has a few limitations to be aware of when planning your deployment.

Next Steps

• Full Configuration Reference — All rate limit fields and strategies
• Auth Shield — Brute-force protection for login endpoints
• WAF Configuration — Web Application Firewall rules and modes
• Dashboard — Explore the Rate Limits page and other dashboard features