README.md

Consul-backed HAProxy Load Balancer

To build & run direct from this Gist, run the following commands:

docker build -t consul-haproxy https://gist.github.com/229668c0466b840e8e8e816bc9ed9ec5.git
docker run --rm -it -p 9000:9000 -p 8000:8000 consul-haproxy

• View the load-balanced site at: http://0.0.0.0:8000/
• View the haproxy statistics page: http://0.0.0.0:9000/haproxy_stats (with username access and password secret)

How it works

This uses the demo.consul.io nyc3 Consul cluster, which has web service with multiple nodes attached. If/when nodes are added/removed, or any of the Consul template values change, the load balancer is automatically reloaded gracefully with the new values using consul-template by sending haproxy a SIGHUP kill signal.

Dockerfile

FROM haproxy:1.7

ENV CT_VERS=0.16.0 \
    CONSUL_HTTP_ADDR=demo.consul.io

RUN  apt-get update \
  && apt-get -y install --no-install-recommends curl ca-certificates unzip \
  && curl -O https://releases.hashicorp.com/consul-template/${CT_VERS}/consul-template_${CT_VERS}_linux_amd64.zip \
  && unzip consul-template_${CT_VERS}_linux_amd64.zip \
  && mv consul-template /usr/local/bin/ \
  && apt-get -y remove --purge curl ca-certificates unzip \
  && apt-get -y autoremove --purge \
  && rm -rf consul* /var/lib/apt/lists/*

COPY haproxy.cfg.tmpl /usr/local/src/
COPY start.sh         /usr/local/bin/

CMD ["/usr/local/bin/start.sh"]

haproxy.cfg.tmpl

global
    daemon
    maxconn {{key "service/haproxy/maxconn"}}

defaults
    mode {{key "service/haproxy/mode"}}{{range ls "service/haproxy/timeouts"}}
    timeout {{.Key}} {{.Value}}{{end}}

listen stats
    bind *:9000

    stats uri /haproxy_stats
    stats realm HAProxy\ Statistics
    stats auth access:secret
    stats admin if TRUE

listen http-in
    bind *:8000{{range service "web"}}
    server {{.Node}} {{.Address}}:{{.Port}}{{end}}

start.sh

#!/bin/bash

[ -z $CONSUL_HTTP_ADDR ] && echo "Consul HTTP address is required" && exit 1

exec consul-template \
  -template "/usr/local/src/haproxy.cfg.tmpl:/usr/local/etc/haproxy/haproxy.cfg" \
  -exec "./docker-entrypoint.sh haproxy -f /usr/local/etc/haproxy/haproxy.cfg"