redis如何实现分布式限流

Redis可以使用令牌桶算法来实现分布式限流。令牌桶算法是一种常用的限流算法，它通过维护一个固定容量的令牌桶，每秒钟往桶里放入一定数量的令牌。当请求到达时，如果令牌桶中有足够的令牌，那么允许请求通过并消耗一个令牌；如果令牌桶中没有足够的令牌，则拒绝请求。

以下是使用Redis实现分布式限流的步骤：

使用Redis的Lua脚本编写一个令牌桶算法的限流器。Lua脚本可以在Redis服务器端执行，可以保证原子性。以下是一个简单的令牌桶算法的Lua脚本示例：

local key = KEYS[1]local capacity = tonumber(ARGV[1])local rate = tonumber(ARGV[2])local now = tonumber(ARGV[3])local tokens_key = key .. ":tokens"local timestamp_key = key .. ":timestamp"local tokens = tonumber(redis.call("get", tokens_key))if not tokens thentokens = capacityendlocal last_refreshed = tonumber(redis.call("get", timestamp_key))if not last_refreshed thenlast_refreshed = nowendlocal delta = math.max(0, now - last_refreshed)local filled_tokens = math.min(capacity, tokens + delta * rate)local allowed = filled_tokens >= 1local new_tokens = filled_tokenslocal new_timestamp = last_refreshedif allowed thennew_tokens = filled_tokens - 1new_timestamp = nowendredis.call("set", tokens_key, new_tokens)redis.call("set", timestamp_key, new_timestamp)return allowed

在代码中调用该Lua脚本，传入限流器的唯一标识符、限流器的容量、限流器的速率以及当前时间戳作为参数，获取限流结果。

import redis.clients.jedis.Jedis;import redis.clients.jedis.JedisPool;public class RedisRateLimiter {private JedisPool jedisPool;public RedisRateLimiter(JedisPool jedisPool) {this.jedisPool = jedisPool;}public boolean allowRequest(String key, int capacity, int rate) {try (Jedis jedis = jedisPool.getResource()) {long now = System.currentTimeMillis();Object result = jedis.eval("local key = KEYS[1]\n" +"local capacity = tonumber(ARGV[1])\n" +"local rate = tonumber(ARGV[2])\n" +"local now = tonumber(ARGV[3])\n" +"\n" +"local tokens_key = key .. \":tokens\"\n" +"local timestamp_key = key .. \":timestamp\"\n" +"\n" +"local tokens = tonumber(redis.call(\"get\", tokens_key))\n" +"if not tokens then\n" +"tokens = capacity\n" +"end\n" +"\n" +"local last_refreshed = tonumber(redis.call(\"get\", timestamp_key))\n" +"if not last_refreshed then\n" +"last_refreshed = now\n" +"end\n" +"\n" +"local delta = math.max(0, now - last_refreshed)\n" +"local filled_tokens = math.min(capacity, tokens + delta * rate)\n" +"local allowed = filled_tokens >= 1\n" +"\n" +"local new_tokens = filled_tokens\n" +"local new_timestamp = last_refreshed\n" +"if allowed then\n" +"new_tokens = filled_tokens - 1\n" +"new_timestamp = now\n" +"end\n" +"\n" +"redis.call(\"set\", tokens_key, new_tokens)\n" +"redis.call(\"set\", timestamp_key, new_timestamp)\n" +"\n" +"return allowed",1,key,Integer.toString(capacity),Integer.toString(rate),Long.toString(now));return (Boolean) result;}}}

在需要进行限流的地方调用RedisRateLimiter的allowRequest方法进行

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