container-app-conf

container-app-conf is a library to easily read application configuration values from multiple sources (YAML, env) while providing type validation.

The initial purpose of this library was to have an easy way to configure an application running inside of a container using environment variables (Docker in this case) and still provide the possibility to use a more simple form of configuration like a YAML file.

container-app-conf is used by

• InfiniteWisdom
• DeineMudda
• py-image-dedup

and hopefully many others :)

How to use

pip install container-app-conf

Extend ConfigBase base

from container_app_conf import ConfigBase
from container_app_conf.entry.string import StringConfigEntry

class AppConfig(ConfigBase):

    MY_CONFIG = StringConfigEntry(
        description="This is just a demo text config entry",
        example="example",
        key_path=[
            "my_app",
            "example"
        ],
        none_allowed=False)

Config Types

If none of the existing types suit your needs you can easily create your own by extending the ConfigEntry base class.

Default Values

A default value can be specified for every ConfigEntry by using the default constructor parameter.

Allow None

By default a None value is only allowed if the default value is None. This means it is not possible to set the MY_CONFIG entry in the example at the top to None even after initial parsing. Specifying an empty text in the yaml or corresponding environment variable will result in an exception. If you want to allow setting a None value even if the default value is not None, use the none_allowed=True constructor parameter.

Data sources

container-app-conf supports the simultaneous use of multiple data sources to determine configuration values. The following implementations are available:

EnvSource

ENV Key

Since you only specify the key path of a config entry the ENV key is generated automatically by concatenating all key path items using an underscore and converting to uppercase:

key_path = ["my_app", "example"]
env_key = "_".join(key_path).upper()

yields MY_APP_EXAMPLE.

YamlSource

File paths

By default the YamlSource looks for a YAML config file in multiple directories that are commonly used for configuration files which include:

• ./
• ~/.config/
• ~/

This can be customized using the path constructor parameter:

from container_app_conf.source.yaml_source import YamlSource
yaml_source = YamlSource(file_name="myapp", path=["/my/path", "/my/other/path"])

Singleton

By default every Config subclass instance will behave like a singleton. This means if you change the config value in one instance it will also affect all other instances of the same __class__.

To be able to create multiple instances of a config that are independent of one another this behaviour can be disabled using the singleton constructor parameter:

config1 = AppConfig(singleton=False)
config2 = AppConfig(singleton=False)

Generate reference config

container-app-conf will (by default) generate a reference config for each data source that supports it. This reference contains all available configuration options. If a default was specified for an entry it will be used, otherwise the example value.

Where and how the reference fill is stored depends on the data source implementation.

If the generated reference contains values that do not make sense because of application constraints, specify your own example or better yet default value using the respective config entry constructor parameter.

Contributing

GitHub is for social coding: if you want to write code, I encourage contributions through pull requests from forks of this repository. Create GitHub tickets for bugs and new features and comment on the ones that you are interested in.

License

container-app-conf
Copyright (c) 2019 Markus Ressel

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.