SpringGateway - Redis限流元件之Luau指令碼&Java實現

在Spring Cloud Gateway中，限流作為閘道器最基本的功能，Spring Cloud Gateway官方就提供了RequestRateLimiterGatewayFilterFactory這個類，適用Redis和lua指令碼實現了令牌桶的方式。

具體實現邏輯在RequestRateLimiterGatewayFilterFactory類中,預設呼叫引數如下：

List<String> keys = getKeys(id);

// The arguments to the LUA script. time() returns unixtime in seconds.
List<String> scriptArgs = Arrays.asList(replenishRate + "", burstCapacity + "",
					Instant.now().getEpochSecond() + "", "1");

// allowed, tokens_left = redis.eval(SCRIPT, keys, args)
Flux<List<Long>> flux = this.redisTemplate.execute(this.script, keys, scriptArgs);

static List<String> getKeys(String id) {
		// use `{}` around keys to use Redis Key hash tags
		// this allows for using redis cluster

		// Make a unique key per user.
		String prefix = "request_rate_limiter.{" + id;

		// You need two Redis keys for Token Bucket.
		String tokenKey = prefix + "}.tokens";
		String timestampKey = prefix + "}.timestamp";
		return Arrays.asList(tokenKey, timestampKey);
}

lua指令碼在Scripts資料夾下：request_rate_limitter.lua

local tokens_key = KEYS[1]
local timestamp_key = KEYS[2]
--redis.log(redis.LOG_WARNING, "tokens_key " .. tokens_key)

local rate = tonumber(ARGV[1])
local capacity = tonumber(ARGV[2])
local now = tonumber(ARGV[3])
local requested = tonumber(ARGV[4])

local fill_time = capacity/rate
local ttl = math.floor(fill_time*2)

--redis.log(redis.LOG_WARNING, "rate " .. ARGV[1])
--redis.log(redis.LOG_WARNING, "capacity " .. ARGV[2])
--redis.log(redis.LOG_WARNING, "now " .. ARGV[3])
--redis.log(redis.LOG_WARNING, "requested " .. ARGV[4])
--redis.log(redis.LOG_WARNING, "filltime " .. fill_time)
--redis.log(redis.LOG_WARNING, "ttl " .. ttl)

local last_tokens = tonumber(redis.call("get", tokens_key))
if last_tokens == nil then
  last_tokens = capacity
end
--redis.log(redis.LOG_WARNING, "last_tokens " .. last_tokens)

local last_refreshed = tonumber(redis.call("get", timestamp_key))
if last_refreshed == nil then
  last_refreshed = 0
end
--redis.log(redis.LOG_WARNING, "last_refreshed " .. last_refreshed)

local delta = math.max(0, now-last_refreshed)
local filled_tokens = math.min(capacity, last_tokens+(delta*rate))
local allowed = filled_tokens >= requested
local new_tokens = filled_tokens
local allowed_num = 0
if allowed then
  new_tokens = filled_tokens - requested
  allowed_num = 1
end

--redis.log(redis.LOG_WARNING, "delta " .. delta)
--redis.log(redis.LOG_WARNING, "filled_tokens " .. filled_tokens)
--redis.log(redis.LOG_WARNING, "allowed_num " .. allowed_num)
--redis.log(redis.LOG_WARNING, "new_tokens " .. new_tokens)

redis.call("setex", tokens_key, ttl, new_tokens)
redis.call("setex", timestamp_key, ttl, now)

return { allowed_num, new_tokens }