HAProxy rate limit across overall http requests.

haproxy.md

Here are many examples to limit RPS for each client, at the same time, we also need a way to setup a global request limit.

There are two requirements for this purpose.

1. instead track client ip, we need a global track.
2. assume we want to setup 1k RPS as a global limit, it should alway allow first 1k requests and only cut off the excess parts.

Here is an example,

frontend fe
  bind :80
  
  # we defined a table here and use gpc0 for counting approved access.
  stick-table  type ip  size 100  expire 5s  store gpc0_rate(1s)
  
  # instead track client's ip, use server ip here which always get a single ip address.
  http-request track-sc0 dst

  # define an acl to check whether RPS is greater than 1k.   
  # Acl will be executed when it be called in an action below.
  acl abuse fe_req_rate     gt 1000
  
  # always allow the first 1k access.
  acl save  sc_gpc0_rate(0) lt 1000

  # deny all excess access here
  http-request deny deny_status 429 if abuse !save

  # gpc0 += 1 if current access is not excess our limit
  http-request sc-inc-gpc0(0) save

  use_backend servers

backend servers
  server example-server xxx.xxx.xxx.xxx