Services

What are services

As a service we understand a background daemon process that should be running inside the container.

Services available in our images are:

• cron

• dnsmasq

• postfix

• ssh

• supervisor

• syslog-ng

• nginx

• php-fpm

• etc.

Supervisord

The supervisord services is the only service which is an exception because it's the default service that is started by the default entrypoint and command.

Supervisor is a python based process control system which is easy to use and configure. We make use of supervisord to redirect the output of the background processes to stdout or stderr which are collected by the docker logging mechanism.

Usually it's quite complicated to collect service logs as they write into a logging directory which would usually be something /var/log/cron.log. Most users would build a log collector to get the logs out of the containers, but if we redirect the output, there's no need for that.

You can also use the supervisorctl inside the container to restart services:

Service components

Services consist of 3 parts:

• A run-file located under /opt/docker/bin/service.d/${SERVICE}.sh

• A supervisord config-file located under /opt/docker/etc/supervisor.d/${SERVICE}.conf

• A provision-file located under /opt/docker/provision/service.d/${SERVICE}.sh

The services are usually added in the base layer of our images

Enabling services

You can control which services should be available by using the docker-service commands:

RUN docker-service enable cron

This command will first execute the provisioning script and enable the service by modifying the supervisor config file (set autostart=true, default is false).