The Anchor IP, in this case 10.15.0.40, is not going to be available inside the container. By default Dockers are on their own bridge network. In the configuration file, you should bind to all interfaces inside the container.

global
  maxconn 4096
  debug

defaults
  log     global
  mode    tcp
  option  tcplog
  option  dontlognull
  timeout connect 5000
  timeout client  50000
  timeout server  50000

frontend www
  bind    *:80
  default_backend node-fedex

backend node-fedex
  balance leastconn
  server  app-1 $BACKEND_IP_1:8080 check
  server  app-2 $BACKEND_IP_2:8080  check

Then at run time, you will need to bind the container to the Anchor IP rather than the docker0 bridge network. In the example below example, I’ve built an image named “my-haproxy” from the simple Dockerfile:

FROM haproxy:1.5
COPY haproxy.cfg /usr/local/etc/haproxy/haproxy.cfg

To launch this container bound to the Anchor IP, run:

docker run --rm --name haproxy-test -p 10.15.0.40:80:80 my-haproxy