HAProxy Config File Example

haproxy.config

global
  #debug                                   # uncomment to enable debug mode for HAProxy

defaults
  mode http                                # enable http mode which gives of layer 7 filtering
  timeout connect 5000ms                   # max time to wait for a connection attempt to a server to succeed
  timeout client 50000ms                   # max inactivity time on the client side
  timeout server 50000ms                   # max inactivity time on the server side

backend legacy                             # define a group of backend servers to handle legacy requests
  server legacy_server 127.0.0.1:8001      # add a server to this backend

frontend app *:80                          # define what port to listed to for HAProxy
  default_backend legacy                   # set the default server for all request

haproxy_content_switching.config

global
  #debug

defaults
  mode http
  option httpclose                         # close the tcp connection after every request
  timeout connect 5000ms
  timeout client 50000ms
  timeout server 50000ms

backend legacy
  server legacy_server 127.0.0.1:8001

backend rails                              # define a group of backend servers to handle rails requests
  server rails_server 127.0.0.1:8002       # add a server to this backend

frontend app *:80
  default_backend legacy
  acl rails_path path_beg /profile         # acl rule for paths to be handled by the new rails app
  use_backend rails if rails_path          # use rails if the rules match.

This is very helpful but I get please use the 'bind' keyword for listening addresses. Maybe newer versions require a slightly different syntax.

Example from HAProxy documentation here

# Simple configuration for an HTTP proxy listening on port 80 on all
# interfaces and forwarding requests to a single backend "servers" with a
# single server "server1" listening on 127.0.0.1:8000
global
    daemon
    maxconn 256

defaults
    mode http
    timeout connect 5000ms
    timeout client 50000ms
    timeout server 50000ms

frontend http-in
    bind *:80
    default_backend servers

backend servers
    server server1 127.0.0.1:8000 maxconn 32