How to block defined IP addresses on HAProxy

Block defined IP addresses on HAProxy load balancer using simple Access Control List.

HAProxy version.

$ haproxy -v
HA-Proxy version 1.7.5-2 2017/05/17
Copyright 2000-2017 Willy Tarreau 

Default HAProxy configuration.

	log /dev/log	local0
	log /dev/log	local1 notice
	chroot /var/lib/haproxy
	stats socket /run/haproxy/admin.sock mode 660 level admin
	stats timeout 30s
	user haproxy
	group haproxy

	# Default SSL material locations
	ca-base /etc/ssl/certs
	crt-base /etc/ssl/private

	# Default ciphers to use on SSL-enabled listening sockets.
	# For more information, see ciphers(1SSL). This list is from:
	# An alternative list with additional directives can be obtained from
	ssl-default-bind-options no-sslv3

	log	global
	mode	http
	option	httplog
	option	dontlognull
        timeout connect 5000
        timeout client  50000
        timeout server  50000
	errorfile 400 /etc/haproxy/errors/400.http
	errorfile 403 /etc/haproxy/errors/403.http
	errorfile 408 /etc/haproxy/errors/408.http
	errorfile 500 /etc/haproxy/errors/500.http
	errorfile 502 /etc/haproxy/errors/502.http
	errorfile 503 /etc/haproxy/errors/503.http
	errorfile 504 /etc/haproxy/errors/504.http

Create ACL rule inside frontend section to define and block IP addresses.

acl is-blocked-ip src
http-request deny if is-blocked-ip

Sample frontend and backend using the specified ACL rule.

frontend web
  bind :80
  #bind :443 ssl crt /etc/ssl/cert/

  option httplog
  log /dev/log local0 debug

  option forwardfor except
  option forwardfor header X-Real-IP

  #redirect scheme https code 301 if !{ ssl_fc }

  acl is-blocked-ip src
  http-request deny if is-blocked-ip

  acl is-draw hdr_dom(host) -i
  use_backend web-draw-production if is-draw

backend web-draw-production
  mode http
  server draw

deny action will stop the evaluation of the rules, immediately reject the request and return HTTP 403 error code. You can use silent-drop to try silently drop connection on the HAProxy, it won't notify client, also any stateful devices placed between the client and HAProxy load balancer will also keep this connection established.