configurability

Background

We host containers running pre-defined images which we maintain on behalf of our customers.

The containers are often running apps like apache, nginx, php or mysql.

Our customers do not have root access or the facility to supply the image themselves (as we manage the images). However, they wish to be able to customise the configuration of these applications.

In order to allow customers to specify how their applications are configured, we mount config maps into the image which have their specific requirements to be applied.

This application is built into each image and runs prior to the application being started. It uses it's own configuration (also baked into the image) to tell it which customer config map to read and where to apply it.

This application was originally written in python but in order to minimise the bloat in customer images (as often python and pip were installed only to satisfy support apps the customer wasn't interested in) it was re-written in go.

configurability config

Files describing what needs to be configured are typically stored in

/etc/configurability/<app>.ini

The location of this folder can be altered by setting

CONFIGURABILITY_INTERNAL=/new location/

A php.ini in that folder might contain the following:

[php]
enabled = true
ini_file_path = /etc/php/7.1/fpm/php.ini
configuration_file_name = configuration-php.json

Where

• 'enabled' means this app should apply these customisations (if true)
• 'ini_file_path' is the file that needs editing and
• 'configuration_file_name' is the name of the file with the custom values in

A full set of example configurability config files can be found in

testfiles/etc_configuration

Nginx and Apache don't specify config files as we only allow customers to edit gzip level and the document root.

Configuration files are searched for in the folder determined by:

$CONFIGURABILITY_DIR

A typical 'configuration-apache2.json' file would contain:

{"gzip":"3","document_root":"mysite/html"}

A full set of example customisation files can be found in

testfiles/customisation

Building and Testing

It should be possible to type

make

which should create

bin/
├── configurator
└── plugins
    ├── apache2.so
    ├── basic.so
    ├── mysql.so
    ├── nginx.so
    └── php.so

If you want to test the configurator it will be necessary to set the following environment variables:

export CONFIGURABILITY_DIR=testfiles/customisations
export CONF_PLUGIN_FOLDER=bin/plugins
export CONFIGURABILITY_INTERNAL=testfiles/etc_configuration
export TEST_INPUT_FOLDER=testfiles/source_config
export TEST_OUTPUT_FOLDER=testfiles/output

NOTE: Under normal operation $TEST_OUTPUT_FOLDER and $TEST_INPUT_FOLDER should not be set.

The values in the testfiles/customisations/ files can be edited to see the effect on the resultant files. Sample source files are provided in the testfiles/source_config folder.

Finally, just run the configurator and compare the contents of /tmp/output to the original source files and the customisations.

Vending

Vending is done using dep for go https://golang.github.io/dep/