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Redtruck

Redtruck is a HAProxy load balancer that is dynamically configured using Serf. It looks for other instances running Serf in the same discovery cluster name and adds them to the HAProxy configuration. It is designed to be run on each Docker host to provide a frontend to multiple instances of your application running on the same host.

Configuration

Configuration happens through environment variables. The following are available:

  • SERF_CLUSTER=myapp - The Serf cluster to join using mDNS.
  • SERF_ROLE=balancer - The Serf role to assign your balancers. Nodes in this role are ignored by the Serf event handler scripts.
  • MATCH_NODE_ROLE=appserv - The Serf role to match for when adding nodes to HAProxy.
  • SYSLOG_SERVER=logs.papertrailapp.com - A UDP syslog host to send event logs to.
  • SYSLOG_PORT=37923 - The syslog server UDP port.
  • SYSLOG_TAG=redtruck - The syslog application name.
  • NODE_PORT=7474 - Port that HAProxy will connect to for your backend application when a node is added.

An example environment file named redtruck.env might look like:

SERF_CLUSTER=myapp
SERF_ROLE=balancer
MATCH_NODE_ROLE=appserv
SYSLOG_SERVER=logs.papertrailapp.com
SYSLOG_PORT=37923
SYSLOG_TAG=redtruck
NODE_PORT=7474

Which can be passed at container run time with --env-file.

Running

Only one Redtruck instance should be run one a given Docker host per SERF_CLUSTER. If you have multiple applications per host, you should set SERF_CLUSTER per application and run one Redtruck instance for each application.

The quickest way to get started is by pulling the image already built from this repository:

docker pull andyshinn/redtruck

Then run with your environment file (see Configuration section above):

docker run -d -p 8040:8040 --env-file redtruck.env andyshinn/redtruck

You will likely want to customize the HAProxy configuration file. Backend nodes will be added to the bottom of the file:

docker run -d -p 8040:8040 --env-file redtruck.env -v /path/to/my/haproxy.cfg:/etc/haproxy/haproxy.cfg andyshinn/redtruck