Configuration

Build-in Config Files

Railgun comes along with some built-in config files:

railgun
|-- railgun
|   |-- website
|   |   +-- webconfig.py
|   +-- runner
|       +-- runconfig.py
+-- config.py

The config.py, railgun/website/webconfig.py and railgun/runner/runconfig.py are build-in config files which are version controlled by git. They define the basic yet default values of the configuration items.

These 3 config files are targeted to different part of the system. config.py determines the behaviour of all components, including the Common Library, the Website Package, the Runner Queue, the Runner Host Library and even the Credential Server.

In addition to config.py, the Website Package takes railgun/website/webconfig.py as the extra config file. It can overwrite the values in config.py. Similarly, the Runner Queue takes railgun/runner/runconfig.py as the extra config file.

Customize the Config Files

The build-in files provides a basis of the configuration values. However, it’s not convenient to edit these files directly, since they are version controlled by git. To ease the deployment, I introduced the custom config directory, where all subfiles will not be tracked by git:

railgun
+-- config
    |-- general.py
    |-- website.py
    +-- runner.py

There are 3 files under config directory. The general.py will overwrite all values in config.py, the website.py will overwrite railgun/website/webconfig.py, and the runner.py will overwrite railgun/runner/runconfig.py.

Be careful when you are playing with general.py! Remember, it can only overwrite the values in config.py, not railgun/website/webconfig.py or railgun/runner/runconfig.py. For example, if you store the following content in general.py:

DEBUG = True

It will not affect the DEBUG value in railgun/website/webconfig.py.

Access the Config in Code

Given the organization of the config files, you should have different ways to access the config value in different parts of the system.

In the Common Library, the Runner Host Library and the Credential Server, you should import config module and access the config attributes, for example:

import config

print config.WEBSITE_BASEURL

In the Runner Queue, you should import runconfig instead of config, for example:

from railgun.runner import runconfig

print runconfig.BROKER_URL

In the Website Package, things become a bit more different. You should access the config values via app instead of the webconfig module. For example:

from railgun.website.context import app

print app.config['SQLALCHEMY_DATABASE_URI']

The way to access the config is very important! You should always use the correct way to read these values.