Merge branch 'master' of github.com:echohead/cornfig

README.md

@@ -1,13 +1,13 @@
 cornfig
 =======
 
-Apply configuration from cloud metadata.
+Apply cornfiguration from cloud metadata.
 
 
 # What does it do?
 
-it turns a cloud-metdata file like this:
-```
+it turns a cloud-metadata file like this:
+```javascript
 {"config": {"keystone": {"database": {"host": "127.0.0.1", "user": "keystone", "password": "foobar"}}}}
 ```
 into service config files like this:
@@ -17,7 +17,7 @@ connection = mysql://keystone:foobar@127.0.0.1/keystone
 ...other settings...
 ```
 
-# But HOW??
+# but... but HOW??
 
 Just pass it the path to a directory tree of templates:
 ```
@@ -40,11 +40,13 @@ e.g.
 ```
 
 If a template is executable it will be treated as an **executable template**.
-Otherwise, it will be treated as a **moustache template**.
+Otherwise, it will be treated as a **mustache template**.
 
-## Moustache Templates
+## Mustache Templates
 
-If you don't need any logic, just some string substitution, use a moustache template:
+If you don't need any logic, just some string substitution, use a mustache template.
+
+Metadata settings are accessed with dot ('.') notation:
 
 ```
 [sql]
@@ -53,16 +55,44 @@ connection = mysql://{{keystone.database.user}}:{{keystone.database.password}@{{
 
 ## Executable Templates
 
-An executable template is a script which accepts parameters in environment variables, and writes a config file to standard out.
+Configuration requiring logic is expressed in executable templates.
+
+An executable template is a script which accepts parameters via environment variables or standard in, and writes a config file to standard out.
 
 The output of the script will be written to the path corresponding to the executable template's path in the template tree.
 
 e.g.
-```
+```bash
 #/bin/sh
 echo "[sql]"
 echo "connection = mysql://$keystone_database_user:$keystone_database_password@$keystone_database_user/keystone"
 ```
 
+TODO: the script is passed the contents of the metadata file on stdin, so you can use a higher-level languages, too:
+```ruby
+#!/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:
+```ruby
+#!/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)
+```
 

cornfig/cornfig.py

@@ -22,6 +22,7 @@ def write_file(path, contents):
   out.write(contents)
   out.close()
 
+# return a map of filenames->filecontents
 def build_tree(templates, config):
   res = {}
   for in_file, out_file in templates:
@@ -50,6 +51,8 @@ def render_executable(path, config):
 def read_config(path):
   return json.loads(open(path).read())
 
+# flatten a nested hash into a one-level hash
+# {x: {a: b} } => {x.a: b}
 def flatten(d, prefix='', res=None):
   res = res or {}
   for k, v in d.items():