This container updates an HAProxy config template periodically using the results of DNS resolution to trigger the update and apply the template and reload HAProxy.

You can either run this container directly by mounting a template file at /etc/haproxy.cfg.tpl or by copying and baking the template file in using a new Dockerfile. Either way it requires an environment variable SERVICE_HOSTNAME which is the DNS name to resolve when updating the template. Multiple DNS hostnames may be specified separated by commas.

Rsyslog is installed in order to provide syslog messages from haproxy on stdout. It can be disabled by setting the RSYSLOG environment variable to n. In order to use it your HAProxy config should look like something like this:

global log 127.0.0.1 local0 notice defaults log global 

Run directly:

$ docker run \ -e SERVICE_HOSTNAME=tasks.galera \ -e UPDATE_FREQUENCY=10 \ -v /foo/galera-haproxy.cfg.tpl:/etc/haproxy.cfg.tpl \ colinmollenhour/haproxy-service 

Or as a new image:

FROM colinmollenhour/haproxy-service COPY galera-haproxy.cfg.tpl /etc/haproxy.cfg.tpl ENV SERVICE_HOSTNAME tasks.galera ENV UPDATE_FREQUENCY 10 

Any block of text between the markers {{HOSTS}} and {{/HOSTS}} (must be on separate lines) will be rendered in-place for each IP resolved by the SERVICE_HOSTNAME. The variables $ip and $num (the last octet of the $ip) will be replaced accordingly. The IP addresses will always be sorted in the same order. There may be multiple {{HOSTS}} ... {{/HOSTS}} blocks in the same template file.

Example:

default-server inter 1s {{HOSTS}} server node${num} ${ip}:3306 check {{/HOSTS}} 

If the SERVICE_HOSTNAME resolves to 10.0.0.12 and 10.0.0.20 it would render:

default-server inter 1s server node12 10.0.0.12:3306 check server node20 10.0.0.20:3306 check 

If you need to run some basic scripts on init before the first template render mount or add a file at /docker-entrypoint-init.sh which will be sourced by docker-entrypoint.sh once on startup.