understanding rate limit

rohit.c.joshi · 2016-08-03T13:28:48+00:00

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understanding rate limit

rohit.c.joshi

Hello,

I am trying to understand the openresty rate limit based on the nginx example given below.

limit_req_zone $binary_remote_addr zone= blitz:10m rate=5r/s;

location /search/ {
   limit_req zone= blitz burst=1;
}

Here my understanding is that nginx will allow upto 5 request before delaying and 6 requests before rejecting it.   Is it correct?
In my test, I am sending 10 requests in a loop and seeing 1 delayed and 8 rejected. 

delaying request, excess: 0.995, by zone "blitz"
limiting requests, excess: 1.900 by zone "blitz"

If I change the nginx code in https://github.com/nginx/nginx/blob/master/src/http/modules/ngx_http_limit_req_module.c#L412 from

if ((ngx_uint_t) excess > limit->burst) to

if ((ngx_uint_t) excess > (limit->burst + ctx->rate))

It works as I described my expectations. Is my understanding incorrect or there is a bug in the code?

rohit.c.joshi

It seems it is honoring only burst limit and not the combination of rate_limit + burst.

On Wednesday, 3 August 2016 01:28:48 UTC-4, RJoshi wrote:

Hello,

I am trying to understand the openresty rate limit based on the nginx example given below.

limit_req_zone $binary_remote_addr zone= blitz:10m rate=5r/s;

location /search/ {
   limit_req zone= blitz burst=1;
}

Here my understanding is that nginx will allow upto 5 request before delaying and 6 requests before rejecting it.   Is it correct?
In my test, I am sending 10 requests in a loop and seeing 1 delayed and 8 rejected. 

delaying request, excess: 0.995, by zone "blitz"
limiting requests, excess: 1.900 by zone "blitz"

If I change the nginx code in https://github.com/nginx/nginx/blob/master/src/http/modules/ngx_http_limit_req_module.c#L412 from

if ((ngx_uint_t) excess > limit->burst) to

if ((ngx_uint_t) excess > (limit->burst + ctx->rate))

It works as I described my expectations. Is my understanding incorrect or there is a bug in the code?

luis.gasca

Offtopic, but I ended up using lua-resty-limit-traffic[1]. Works as advertised.

Luis

[1] https://github.com/openresty/lua-resty-limit-traffic

El 03/08/2016 a las 7:30, RJoshi escribió:

It seems it is honoring only burst limit and not the combination of rate_limit + burst.

On Wednesday, 3 August 2016 01:28:48 UTC-4, RJoshi wrote:

Hello,

I am trying to understand the openresty rate limit based on the nginx example given below.

limit_req_zone $binary_remote_addr zone= blitz:10m rate=5r/s;

location /search/ {
   limit_req zone= blitz burst=1;
}
Here my understanding is that nginx will allow upto 5 request before delaying and 6 requests before rejecting it.   Is it correct?
In my test, I am sending 10 requests in a loop and seeing 1 delayed and 8 rejected. 
delaying request, excess: 0.995, by zone "blitz"
limiting requests, excess: 1.900 by zone "blitz"

If I change the nginx code in https://github.com/nginx/nginx/blob/master/src/http/modules/ngx_http_limit_req_module.c#L412 from

if ((ngx_uint_t) excess > limit->burst) to

if ((ngx_uint_t) excess > (limit->burst + ctx->rate))

It works as I described my expectations. Is my understanding incorrect or there is a bug in the code?

rohit.c.joshi

Thanks Luis. I have looked at this earlier but was not sure it is ready for production as it has "This library is already usable though still highly experimental."

Have you compared any performance impact or memory growth?

On Wednesday, 3 August 2016 04:01:31 UTC-4, Luis Gasca wrote:

Offtopic, but I ended up using lua-resty-limit-traffic[1]. Works as advertised.

Luis

[1] https://github.com/openresty/lua-resty-limit-traffic

El 03/08/2016 a las 7:30, RJoshi escribió:
It seems it is honoring only burst limit and not the combination of rate_limit + burst.

On Wednesday, 3 August 2016 01:28:48 UTC-4, RJoshi wrote:
Hello,
I am trying to understand the openresty rate limit based on the nginx example given below.
limit_req_zone $binary_remote_addr zone= blitz:10m rate=5r/s;
location /search/ {
   limit_req zone= blitz burst=1;
}
Here my understanding is that nginx will allow upto 5 request before delaying and 6 requests before rejecting it.   Is it correct?
In my test, I am sending 10 requests in a loop and seeing 1 delayed and 8 rejected. 
delaying request, excess: 0.995, by zone "blitz"
limiting requests, excess: 1.900 by zone "blitz"
If I change the nginx code in https://github.com/nginx/nginx/blob/master/src/http/modules/ngx_http_limit_req_module.c#L412 from

if ((ngx_uint_t) excess > limit->burst) to

if ((ngx_uint_t) excess > (limit->burst + ctx->rate))

It works as I described my expectations. Is my understanding incorrect or there is a bug in the code?
.

luis.gasca

I haven't done any formal comparison, but the impact in our system is minimal, hardly noticeable. Note that our system handles 500-800 requests/sec at peak. Maybe with higher traffic the impact would be different

El 03/08/2016 a las 15:30, RJoshi escribió:

Thanks Luis. I have looked at this earlier but was not sure it is ready for production as it has "This library is already usable though still highly experimental."

Have you compared any performance impact or memory growth?

On Wednesday, 3 August 2016 04:01:31 UTC-4, Luis Gasca wrote:

Offtopic, but I ended up using lua-resty-limit-traffic[1]. Works as advertised.

Luis

[1] https://github.com/openresty/lua-resty-limit-traffic

El 03/08/2016 a las 7:30, RJoshi escribió:

It seems it is honoring only burst limit and not the combination of rate_limit + burst.

On Wednesday, 3 August 2016 01:28:48 UTC-4, RJoshi wrote:

Hello,
I am trying to understand the openresty rate limit based on the nginx example given below.

limit_req_zone $binary_remote_addr zone= blitz:10m rate=5r/s;

location /search/ { limit_req zone= blitz burst=1; }
Here my understanding is that nginx will allow upto 5 request before delaying and 6 requests before rejecting it. Is it correct?
In my test, I am sending 10 requests in a loop and seeing 1 delayed and 8 rejected.
delaying request, excess: 0.995, by zone "blitz"
limiting requests, excess: 1.900 by zone "blitz"

If I change the nginx code in https://github.com/nginx/nginx/blob/master/src/http/modules/ngx_http_limit_req_module.c#L412 from

if ((ngx_uint_t) excess > limit->burst) to

if ((ngx_uint_t) excess > (limit->burst + ctx->rate))

It works as I described my expectations. Is my understanding incorrect or there is a bug in the code?

.