I am using "ngx_http_limit_req" module. After going through the code I see that if "burst = 0" (i.e. not specified) then maximum rate limiting that can be offered is 1000 RPS only. I have seen this in my stress test too.
I didn't see this in any documentation. Want to clarify if this is really true or I missed something?

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Reasoning :
1. Module expects uniform request arrival. Any request that breaks the uniformity, will get rate limited.
2. Configured rate = 1000r/s. This means 1 request-per-ms.
3. If more than 1 request is received in same "ms" time, then only 1 request is served. All other requests are rate limited.
4. For above configuration, if "burst=X" is configured, then "X" number of requests are served while requests more than that will get rate limited.
5. If Configured rate = 2000r/s (i.e. 2 request-per-ms). If "burst=0" (i.e. not specified), then too it supports only 1-request-per-ms rate. If 3 requests are received in same "ms" then only 1 is served and other 2 are rate limited.