ruerate

ruelimit implements high-performance rate limiting algorithms with both in-memory Golang and distributed Redis implementations.

Distributed variants built on top of redis/rueidis with auto-pipelining. The in-memory variants use a sharded lockable map.

Godoc

Features

1. Zero memory default: Only limiters out of their default state use memory. Automatic cleanup via TTLs.
2. Keyed limiters: Apply limits per-identifier (e.g. http requests by IP)
3. Replenishable: Manually add tokens back to the bucket on-demand (token bucket algorithm)
4. Local caching: RedisCacheable* variants avoid round-trips when a limiter is known to be exhausted
5. Very low allocation: Most paths are zero-alloc, others are 1 alloc.

Usage

Token Bucket Algorithm

Use-cases: API rate limiting, protecting from traffic spikes, and scenarios requiring a steady flow of requests with occasional bursts.

Implementations:

• tokenbucket.LocalLimiter: Single-resource in-memory limiter.
• tokenbucket.LocalKeyedLimiter: Per-key in-memory limiter.
• tokenbucket.RedisLimiter: Distributed, replenishable single-resource limiter.
• tokenbucket.RedisKeyedLimiter: Distributed, replenishable per-key limiter.
• tokenbucket.RedisCacheableLimiter: More efficient version of RedisLimiter with client-side caching.
• tokenbucket.RedisCacheableKeyedLimiter: More efficient version of RedisKeyedLimiter with client-side caching.

Configuration

The tokenbucket.LimiterOpts struct defines the bucket behavior:

type LimiterOpts struct {
    RatePerSec float64 // How many tokens are added to the bucket per second
    Capacity   int64   // Maximum tokens the bucket can hold
}

Example

// Scenario: Allow 1 HTTP request per IP every second, with a burst of up to 100.
//
// Use distributed, Redis-backed variant so limits apply across frontend server pool.
lim, _ := tokenbucket.RedisCacheableKeyedLimiter(
    rueidisClient,
    tokenbucket.DefaultRedisKeyedLimiterOpts(
        "http_requests_by_ip", // limiter name, used to derive Redis key
        LimiterOpts{
            RatePerSec: ruerate.Every(time.Second), 
            Capacity: 100,
        }
    )
)

// Check if this IP is allowed to make another HTTP request
ok, wait, _ := lim.Allow(context.TODO(), "10.0.0.1")

if !ok {
    // Not allowed -- no tokens left in the bucket
    // Next token available after 'wait'
    w.WriteHeader(http.StatusTooManyRequests)
    // You probably want to apply jitter. This will add rand(0-50%) jitter.
    wait = ruerate.WithJitter(wait, 0.5)
    w.Header().Set("X-RateLimit-Remaining-Ms", strconv.FormatInt(wait.Milliseconds(), 10))
}

// Handle the request...

Exponential Backoff, Linear Decay Algorithm

Use-cases: Jailing spammy clients, slowing down brute-force login attempts, or building polite client-side reconnection loops, i.e. with the local in-memory variants.

Implementations:

• backoff.LocalLimiter: Single resource in-memory backoff limiter
• backoff.LocalKeyedLimiter: Per-key in-memory backoff limiter
• backoff.RedisLimiter: Distributed, single resource backoff limiter
• backoff.RedisKeyedLimiter: Distributed, per-key backoff limiter

Configuration

The backoff.LimiterOpts struct defines the bucket behavior:

type LimiterOpts struct {
    BaseWait              time.Duration // Minimum wait between attempts
    MaxWait               time.Duration // Maximum "lockout" duration
    PenaltyDecayInterval  time.Duration // How long prior attempts take to be "forgotten"
    GrowthFactor          float64       // How fast backoff grows. 2.0 doubles each time.
}

Example (server)

// Scenario: Game server should punish overly frequent reconnections, based on UserID.
// Users shouldn't be reconnecting more often than once per 30 mins (in the long run)
// Be tolerant to occasional reconnects, but quickly ramp "punishment" for too many.
lim, _ := backoff.NewLocalKeyedLimiter(
    backoff.LimiterOpts{
        // Minimum wait of 5s between attempts. Wait grows from here.
        BaseWait: 5 * time.Second,
		
        // Users can be "locked out" for a maximum of 300s
        MaxWait: 300 * time.Second,
		
        // Prior attempts take 30m to be forgotten (linear decay)
        PenaltyDecayInterval: 30 * time.Minute,
        
        // Wait doubles each time, e.g. 5s, 10s, 20s, 40s, 1m20s, 2m40s etc. (up to MaxWait cap)
        GrowthFactor: 2.0,
    }
)

// Check if this user is allowed to connect right now
ok, wait, _ := lim.Allow(context.TODO(), "timapple")
if !ok {
    // Logic to reject connection, probably applying jitter to wait...
}

Example (client)

// Scenario: Apply back-off when connecting to a server.
// Start at 1s between attempts, and double each time until 32s between attempts.
// Remember failed attempts for 60s, will "cool down" back to 1s after about 5 minutes.
lim, _ := backoff.NewLocalLimiter(
    backoff.LimiterOpts{
        BaseWait: time.Second,
        MaxWait: 32 * time.Second,
        PenaltyDecayInterval: 60 * time.Second,
        GrowthFactor: 2.0,
    }
})

// Connection loop sketch
// Will wait 1s, 2s, 4s, 8s, 16s, 32s, 32s, 32s (-decay)
func DialServerWithBackoff(ctx context.Context, lim *LocalBackoffLimiter) error {
retry:
    ok, wait, _ := lim.Allow(ctx)
    if !ok {
        select {
        case <-time.After(wait):
            goto retry
        case <-ctx.Done():
            return fmt.Errorf("while waiting: %w", err)
        }	
    }
	
    err := server.Dial(ctx)
	if errors.Is(err, ErrServerUnreachable) {
        goto retry
    }
	
    return err
}

Performance

Redis variants are designed to use as little Redis keyspace and storage as possible, and reduce round-trips where possible, via RedisCacheable* variants. These limiters are designed for use in hot paths in production.

By using rueidis auto-pipelining, exceptional throughput is possible, and the simple atomic design makes it simple to scale via hash-slot sharding. Due to pipelining support, benchmarks should be run with high parallelism in order to benchmark the limiter, not RTT. Benchmarks run against Valkey 8.1.x running locally.

tokenbucket algo

goos: linux
goarch: amd64
pkg: github.com/iamcalledrob/ruerate/tokenbucket
cpu: AMD Ryzen 5 8600G w/ Radeon 760M Graphics     

BenchmarkRedisCacheableLimiter
BenchmarkRedisCacheableLimiter/Exhausted_Serial
BenchmarkRedisCacheableLimiter/Exhausted_Serial-12         	 6212396	       190.3 ns/op	       0 B/op	       0 allocs/op
BenchmarkRedisCacheableLimiter/Exhausted_Parallel100
BenchmarkRedisCacheableLimiter/Exhausted_Parallel100-12    	 5814763	       208.5 ns/op	       0 B/op	       0 allocs/op
BenchmarkRedisCacheableLimiter/Allowed_Parallel100
BenchmarkRedisCacheableLimiter/Allowed_Parallel100-12      	  238906	      4725 ns/op	      99 B/op	       1 allocs/op

BenchmarkRedisLimiter
BenchmarkRedisLimiter/Exhausted_Parallel100
BenchmarkRedisLimiter/Exhausted_Parallel100-12    	  347024	      3381 ns/op	      93 B/op	       1 allocs/op
BenchmarkRedisLimiter/Allowed_Parallel100
BenchmarkRedisLimiter/Allowed_Parallel100-12      	  247245	      4706 ns/op	      98 B/op	       1 allocs/op

BenchmarkLocalLimiter
BenchmarkLocalLimiter/Exhausted_Serial
BenchmarkLocalLimiter/Exhausted_Serial-12         	12621777	        98.36 ns/op	       0 B/op	       0 allocs/op
BenchmarkLocalLimiter/Exhausted_Parallel100
BenchmarkLocalLimiter/Exhausted_Parallel100-12    	 9617128	       128.4 ns/op	       0 B/op	       0 allocs/op
BenchmarkLocalLimiter/Allowed_Parallel100
BenchmarkLocalLimiter/Allowed_Parallel100-12      	11479965	       125.3 ns/op	       0 B/op	       0 allocs/op

backoff algo

goos: linux
goarch: amd64
pkg: github.com/iamcalledrob/ruerate/tokenbucket
cpu: AMD Ryzen 5 8600G w/ Radeon 760M Graphics     

BenchmarkRedisLimiter
BenchmarkRedisLimiter/Allow_Serial
BenchmarkRedisLimiter/Allow_Serial-12         	  185803	      6146 ns/op	     102 B/op	       1 allocs/op
BenchmarkRedisLimiter/Allow_Parallel100
BenchmarkRedisLimiter/Allow_Parallel100-12    	  356449	      3164 ns/op	      92 B/op	       1 allocs/op

BenchmarkLocalLimiter
BenchmarkLocalLimiter/Allow_Serial
BenchmarkLocalLimiter/Allow_Serial-12         	15445687	        78.62 ns/op	       0 B/op	       0 allocs/op
BenchmarkLocalLimiter/Allow_Parallel100
BenchmarkLocalLimiter/Allow_Parallel100-12    	11196720	       120.3 ns/op	       0 B/op	       0 allocs/op

BenchmarkLocalKeyedLimiter
BenchmarkLocalKeyedLimiter/Allow_Serial
BenchmarkLocalKeyedLimiter/Allow_Serial-12         	 6896593	       171.1 ns/op	       0 B/op	       0 allocs/op
BenchmarkLocalKeyedLimiter/Allow_Parallel100
BenchmarkLocalKeyedLimiter/Allow_Parallel100-12    	 6183844	       196.1 ns/op	       0 B/op	       0 allocs/op

TODOs

• Migrate to common interface across local and redis token bucket limiters
• MILD backoff algorithm
• Leaky bucket algorithm
• backoff.RedisCacheableLimiter, to avoid any Redis round-trip when a client is known to been locked out.