redis怎么实现分布式限流

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：
1.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主机端执行，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：
```lua
localkey=KEYS[1]
localcapacity=tonumber(ARGV[1])
localrate=tonumber(ARGV[2])
localnow=tonumber(ARGV[3])
localtokens_key=key..":tokens"
localtimestamp_key=key..":timestamp"
localtokens=tonumber(redis.call("get",tokens_key))
ifnottokensthen
tokens=capacity
end
locallast_refreshed=tonumber(redis.call("get",timestamp_key))
ifnotlast_refreshedthen
last_refreshed=now
end
localdelta=math.max(0,now-last_refreshed)
localfilled_tokens=math.min(capacity,tokens+delta*rate)
localallowed=filled_tokens>=1
localnew_tokens=filled_tokens
localnew_timestamp=last_refreshed
ifallowedthen
new_tokens=filled_tokens-1
new_timestamp=now
end
redis.call("set",tokens_key,new_tokens)
redis.call("set",timestamp_key,new_timestamp)
returnallowed
```
2.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。
```java
importredis.clients.jedis.Jedis;
importredis.clients.jedis.JedisPool;
publicclassRedisRateLimiter{
privateJedisPooljedisPool;
publicRedisRateLimiter(JedisPooljedisPool){
this.jedisPool=jedisPool;
}
publicbooleanallowRequest(Stringkey,intcapacity,intrate){
try(Jedisjedis=jedisPool.getResource()){
longnow=System.currentTimeMillis();
Objectresult=jedis.eval(
"localkey=KEYS[1]n"+
"localcapacity=tonumber(ARGV[1])n"+
"localrate=tonumber(ARGV[2])n"+
"localnow=tonumber(ARGV[3])n"+
"n"+
"localtokens_key=key..":tokens"n"+
"localtimestamp_key=key..":timestamp"n"+
"n"+
"localtokens=tonumber(redis.call("get",tokens_key))n"+
"ifnottokensthenn"+
"tokens=capacityn"+
"endn"+
"n"+
"locallast_refreshed=tonumber(redis.call("get",timestamp_key))n"+
"ifnotlast_refreshedthenn"+
"last_refreshed=nown"+
"endn"+
"n"+
"localdelta=math.max(0,now-last_refreshed)n"+
"localfilled_tokens=math.min(capacity,tokens+delta*rate)n"+
"localallowed=filled_tokens>=1n"+
"n"+
"localnew_tokens=filled_tokensn"+
"localnew_timestamp=last_refreshedn"+
"ifallowedthenn"+
"new_tokens=filled_tokens-1n"+
"new_timestamp=nown"+
"endn"+
"n"+
"redis.call("set",tokens_key,new_tokens)n"+
"redis.call("set",timestamp_key,new_timestamp)n"+
"n"+
"returnallowed",
1,
key,
Integer.toString(capacity),
Integer.toString(rate),
Long.toString(now)
);
return(Boolean)result;
}
}
}
```
3.在需要进行限流的地方调用RedisRateLimiter的allowRequest方法进行