How to return 429 error code when limiting HTTP request rate

[Zbyněk Vymazal]

Hello,

I'd like to ask for an advice how return custom HTTP error code when rate limit 
rule is triggered. I have sort of followed the configuration described here: 
http://blog.haproxy.com/2012/02/27/use-a-load-balancer-as-a-first-row-of-defense-against-ddos/
 (Limiting the HTTP request rate) with some modifications and the rate limiting 
works as required.

I'd like to ask if there is a way how to return 429 error instead of 403 as it 
returned now with the rule http-request deny ?

The interesting part of config file looks like this:

frontend:

  stick-table type ip size 10k expire 30s store gpc0

  # Refuse a new connection from an abuser
  tcp-request connection reject if { sc0_get_gpc0 gt 0 }

  # Return a 403 for requests in an established connection
  http-request deny if { sc0_get_gpc0 gt 0 }


backend:

  stick-table type ip size 10k expire 30s store http_req_rate(10s)

  # Parse X-Forwarded-For header and add source IP to the sticky tables for 
request rate control
  tcp-request content track-sc0 hdr_ip(X-Forwarded-For,1) table ft_web
  tcp-request content track-sc1 hdr_ip(X-Forwarded-For,1) table bk_web

  # If the source IP sent 50 or more http requests over the defined period flag 
the IP as an abuser
  acl abuse sc1_http_req_rate gt 50
  acl flag_abuser sc0_inc_gpc0(ft_web) gt 0

  # Return a 403 to the abuser
  http-request deny if abuse flag_abuser

Thanks for help.

Kind Regards,

Zbynek