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HAProxy

What is HAProxy?​

HAProxy is a high-performance TCP/HTTP load balancer widely used to distribute traffic across multiple backend servers. In Laradock it runs as a self-configuring load balancer container, built from the dockercloud/haproxy image, which watches the Docker socket and automatically balances traffic across whatever containers it's linked to.

Start HAProxy​

docker compose up -d haproxy

haproxy/compose.yml links to proxy and proxy2, the two containers created by the Varnish service. Start those first (or alongside it) if you're load-balancing across them:

docker compose up -d proxy proxy2 haproxy

Stop HAProxy​

docker compose stop haproxy

Configuration​

The only setting is in haproxy/defaults.env, overridable by adding the same line to your own .env:

VariableDefaultWhat it does
HAPROXY_HOST_HTTP_PORT8085Host-side port mapped to container port 8085.

There's no site or backend config file to edit directly: the dockercloud/haproxy base image builds its balancing rules automatically from the containers it's linked to (proxy and proxy2 in the shipped compose.yml), by watching /var/run/docker.sock.

How it balances traffic​

HAProxy mounts the Docker socket (/var/run/docker.sock) so it can detect its linked containers' ports at startup and load-balance across them without a static config file. To balance across different containers than the defaults, edit the links: list in haproxy/compose.yml.

Change the exposed port​

HAPROXY_HOST_HTTP_PORT=8090
docker compose up -d haproxy

Common issues​

  • HAProxy starts but has nothing to balance. It only load-balances containers listed under links: in haproxy/compose.yml (proxy and proxy2 by default). Make sure those containers are actually running.
  • Port already in use on your host. Another service is already bound to 8085. Change HAPROXY_HOST_HTTP_PORT and restart.
  • Changes to links: don't seem to apply. dockercloud/haproxy reconfigures on container start by inspecting Docker, so after editing links: you need to recreate the container: docker compose up -d haproxy, not just restart it.

Looking for the containers HAProxy balances by default? See Varnish. New to Laradock? Start with Getting Started.