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cornfig

Apply cornfiguration from cloud metadata.

What does it do?

it turns a cloud-metadata file like this:

{"keystone": {"database": {"host": "127.0.0.1", "user": "keystone", "password": "foobar"}}}

into service config files like this:

[sql]
connection = mysql://keystone:foobar@127.0.0.1/keystone
...other settings...

but... but HOW??

Just pass it the path to a directory tree of templates:

cornfig -t /home/me/my_templates

Templates?

The template directory structure should mimic a root filesystem, and contain templates for only those files you want cornfig-ed.

e.g.

~/my_templates$ tree
.
└── etc
    ├── keystone
    │   └── keystone.conf
    └── mysql
        └── mysql.conf

An example tree can be found here.

If a template is executable it will be treated as an executable template. Otherwise, it will be treated as a mustache template.

Mustache Templates

If you don't need any logic, just some string substitution, use a mustache template.

Metadata settings are accessed with dot ('.') notation:

[sql]
connection = mysql://{{keystone.database.user}}:{{keystone.database.password}@{{keystone.database.host}}/keystone

Executable Templates

Configuration requiring logic is expressed in executable templates.

An executable template is a script which accepts configuration as a json string on standard in, and writes a config file to standard out.

The script should exit non-zero if it encounters a problem, so that cornfig knows what's up.

The output of the script will be written to the path corresponding to the executable template's path in the template tree.

#!/usr/bin/env ruby
require 'json'
params = JSON.parse STDIN.read
puts "connection = mysql://#{c['keystone']['database']['user']}:#{c['keystone']['database']['password']}@#{c['keystone']['database']['host']}/keystone"

You could even embed mustache in a heredoc, and use that:

#!/usr/bin/env ruby
require 'json'
require 'mustache'
params = JSON.parse STDIN.read

template = <<-eos
[sql]
connection = mysql://{{keystone.database.user}}:{{keystone.database.password}}@{{keystone.database.host}}/keystone

[log]
...
eos

# tweak params here...

puts Mustache.render(template, params)

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