Configs

Configs is a helper class to manage config and .env files over different environments,instances,test scenarios and so on

Install

pip3 install DZDConfigs

Dev

pip3 install git+https://git.connect.dzd-ev.de/dzdpythonmodules/configs.git

How to use

tl;tr: You can see a full working example in Configs/smoketest

In short you will use Configs like this:

from Configs import getConfig
config = getConfig()
print(config.MY_CONFIG_VALUE)

There are three possibilites to provide Configs with data.

• In python code "config.py"
• In one or more .env files
• In Environment variables

In future version there will be yaml and json files supported as well

1 : A config.py file

Here you can register values that are controlling your business logic

./config.py:

from Configs import ConfigBase

#define different classes per environment

class DEFAULT(ConfigBase):
    # Always create a DEFAULT class and use it as the base class for other environments classes

    # DEFAULT must have all config variables / class attributes that are used in the other classes
    MY_CONFIG_VALUE=1
    MY_CONFIG_VALUE_B=1

# All following config classes inherit from DEFAULT
class PRODUCTION(DEFAULT):
    MY_CONFIG_VALUE=2

class DEVELOPMENT(DEFAULT):
    MY_CONFIG_VALUE=2

2 : .env files

Here you can register values you dont want to have in a repo (like passwords) or describe connections to external systems (like database hostnames)

⚠ Environment variables need to have the prefix "CONFIGS_" in order to be parsed by Configs

./env/DEFAULT.env:

CONFIGS_MYDB_HOST='LOCALHOST'

./env/PRODUCTION.env:

CONFIGS_MYDB_HOST='THE_PROD_DBHOSTMACHINE.NETWORK.INTERNAL'

⚠ These values will be set as OS environment variable after the getConfig was called.

3 : OS environment variables

Similar like option 2 you can set OS environment variables that do not belong in your repo (like credentials, hostnames etc)

⚠ Environment variables need to have the prefix "CONFIGS_" in order to be parsed by Configs

This is convenient for use with docker (see https://docs.docker.com/compose/environment-variables/ and https://docs.docker.com/engine/reference/commandline/run/ see "--env , -e")

e.g.

>>> docker run -e CONFIGS_APP_PATH="/mypath/isstrong" me/mypythonapp

Will populate the variable APP_PATH in your python code running in your container

from Configs import getConfig
config = getConfig()
print(config.APP_PATH)

This will output /mypath/isstrong

How to use the config instance

./main.py:

import os
# For examples purposes we set an OS environment variables from python
os.environ["CONFIGS_ANOTHER_ENV_VAR"] = "ANOTHER_VALUE"

from Configs import getConfig

# get the config instance
config = getConfig()

# the config variables declared in the classes
print(config.MY_CONFIG_VALUE)
# a config variable from the .env-file vars
print(config.MYDB_HOST)
# a config value from the environment variable we set above
print(config.ANOTHER_ENV_VAR)
# prints: ANOTHER_VALUE

Switch between configurations

To switch the environment set the envrionemt variable ENV. In this example we switch to PRODUCTION

Docker

docker run -e ENV="PRODUCTION"

Linux

export ENV="PRODUCTION"

Windows

setx ENV="PRODUCTION"

Python

For testing purposes you can switch the environemt also from python itself

import os
os.environ["ENV"] = "PRODUCTION"

Keep my envs out of the repo!

Register following pattern in your .gitignore file to prevent you hostnames and passwords landing in git repository

./gitignore:

[...]
.env
!*/env/DEFAULT.env
[...]

⚠️ What else to notice?

Types

Every variable in config.py can have more complex types like custom classes, functions, instances

.env files and environmet variables can only contain following types

• int
• string
• boolean
• json (which will be represent as python dicts)

Who is overriding who

What happens when multiple sources have the same variable name?

For example in your DEFAULT.env:

CONFIGS_MY_HAPPY_OVERRIDE="ENVFILEVAL"

and in your config.py is the same var

class DEFAULT(ConfigBase):
    MY_HAPPY_OVERRIDE = "CONFFILEVAL"

from Configs import getConfig
config = getConfig()
print(config.MY_HAPPY_OVERRIDE)

This will output ENVFILEVAL

Env file values will always override config.py values.

And OS env values will override env file values

If you want env file vars to override allready existing system environment variables you can set the getConfig() parameter env_file_vars_override_system_env_var to True

getConfig(env_file_vars_override_system_env_vars=True)

This is helpfull for testing purposes, when switching the environment on the fly (see Configs/smoketest/main.py)

What is planned for the future

Short term

• Support yaml and json config files
• Support set, update variables from code
• Get meta data on variables (source, overwritten-by)

Long term

• Server-client architecure, making central configuration servers possible