ENV EXtended

envex is a dotenv .env aware environment variable handler with typing features and Hashicorp vault support.

Overview

This module provides a convenient interface for handling the environment, and therefore configuration of any application using 12factor.net principals removing many environment-specific variables and security sensitive information from application code.

An Env instance delivers a lot of functionality by providing a type-smart front-end to os.environ, providing a superset of os.environ functionality, including setting default values.

From version 2.0, this module also supports transparently fetching values from Hashicorp vault, which reduces the need to store secrets in plain text on the filesystem. This functionality is optional, activated automatically when the hvac module is installed, and connection and authentication to Vault succeed. Only get (no set) operations to Vault are supported. Values fetched from Vault are cached by default to reduce the overhead of the api call. If this is of concern to security, caching can be disabled using the enable_cache=False parameter to Env.

This module provides some features not supported by other dotenv handlers (python-dotenv, etc.) including recursive expansion of template variables, which can be very useful for DRY.

from envex import env

assert env['HOME'] == '/Users/username'

env['TESTING'] = 'This is a test'
assert env.get('TESTING') == 'This is a test'
assert env['TESTING'] == 'This is a test'
assert env('TESTING') == 'This is a test'

import os

assert os.environ['TESTING'] == 'This is a test'

assert env.get('UNSET_VAR') is None
env.set('UNSET_VAR', 'this is now set')
assert env.get('UNSET_VAR') is not None
env.setdefault('UNSET_VAR', 'and this is a default value but only if not set')
assert env.get('UNSET_VAR') == 'this is now set'
del env['UNSET_VAR']
assert env.get('UNSET_VAR') is None

Note that there is a subtle difference between env.get(<variable>, default=<default value>) and env(<variable>, default=<default value>). If the variable is unset, the former simply returns the default value, but the latter also sets the value to the default value in the environment.

An Env instance can also read a .env (default name) file and update the application environment accordingly. It can read this either when created with Env(readenv=True) or directly by using the method read_env(). To override the base name of the dot env file, use the DOTENV environment variable. Other kwargs that can be passed to Env when created:

• environ (env): pass the environment to update, default is os.environ, passing an empty dict will create a new env
• readenv (bool): search for and read .env files
• env_file (str): name of the env file, os.environ["DOTENV"] if set, or .env by default
• search_path (str or list): a single path or list of paths to search for the env file search_path may also be passed as a colon-separated list (or semicolon on Windows) of directories to search.
• parents (bool): search (or not) parents of dirs in the search_path
• overwrite (bool): overwrite already set values read from .env, default is to only set if not currently set
• update (bool): push updates os.environ if true (default) otherwise pool changes internally only
• working_dirs (bool): add CWD for the current process and PWD of source .env file
• exception: (optional) Exception class to raise on error (default is KeyError)
• errors: bool whether to raise error on missing env_file (default is False)
• kwargs: (keyword args, optional) additional environment variables to add/override

In addition, Env supports a few HashiCorp Vault configuration parameters:

• url: (str, optional) vault url, default is $VAULT_ADDR
• token: (str, optional) vault token, default is $VAULT_TOKEN or content of ~/.vault-token
• cert: (tuple, optional) (cert, key) path to client certificate and key files
• verify: (bool, optional) whether to verify server cert (default is True)
• base_path: (optional) str base path, or "environment" for secrets (default is None). This is used to prefix the path to the secret, i.e. f"/secret/{base_path}/key".

Some type-smart functions act as an alternative to Env.get and having to parse the result:

from envex import env

env['AN_INTEGER_VALUE'] = 2875083
assert env.get('AN_INTEGER_VALUE') == '2875083'
assert env.int('AN_INTEGER_VALUE') == 2875083
assert env('AN_INTEGER_VALUE', type=int) == 2875083

env['A_TRUE_VALUE'] = True
assert env.get('A_TRUE_VALUE') == 'True'
assert env.bool('A_TRUE_VALUE') is True
assert env('A_TRUE_VALUE', type=bool) is True

env['A_FALSE_VALUE'] = 0
assert env.get('A_FALSE_VALUE') == '0'
assert env.int('A_FALSE_VALUE') == 0
assert env.bool('A_FALSE_VALUE') is False
assert env('A_FALSE_VALUE', type=bool) is False

env['A_FLOAT_VALUE'] = 287.5083
assert env.get('A_FLOAT_VALUE') == '287.5083'
assert env.float('A_FLOAT_VALUE') == 287.5083
assert env('A_FLOAT_VALUE', type=float) == 287.5083

env['A_LIST_VALUE'] = '1,"two",3,"four"'
assert env.get('A_LIST_VALUE') == '1,"two",3,"four"'
assert env.list('A_LIST_VALUE') == ['1', 'two', '3', 'four']
assert env('A_LIST_VALUE', type=list) == ['1', 'two', '3', 'four']

Environment variables are always stored as strings. This is enforced by the underlying os.environ, but also true of any provided environment, which must use the MutableMapping[str, str] contract.

Vault

In addition to handling of the os environment and .env files, Env supports fetching secrets from Hashicorp Vault using the kv.v2 engine. This provides a secure secrets store, without exposing them in plain text on the filesystem and in particular in published docker images. It also prevents storing secrets in the operating system’s environment, which can be inspected by external processes. Env can read secrets from the environment variables if you set Env(readenv=True).

This document does not cover how to set up and configure a vault server, but you can find useful resources on the following websites:

• hashicorp.com for the developer documentation and detailed information and tutorials on setting up and hosting your own vault server, and
• vaultproject.io for information about HashiCorp's managed cloud offering.

To access the vault server, you need a token with a role that has read permission for the path to the secrets. A read only profile is the recommended policy for tokens used at runtime by the application.

This library provides a utility called env2hvac that can import (create or update) a typical .env file into vault. The utility uses a prefix that consists of an application name and an environment name, using the format // - for example, myapp/prod/DB_PASSWORD. The utility requires that the token has a role with create permission for the base secrets path on the vault server. The utility currently assumes that the kv secrets engine is mounted at secret/. The final path where the secrets are stored will be secret/data///.

Environment Variables

The SecretsManager and Vault client leverage environment variables for their configuration. This ensures a degree of transparency as it allows the client to use them but mitigates the need for the client code to be aware of their presence. A summary of these variables is in the following table:

Variable	Description
VAULT_ADDR	The URL of the vault server
VAULT_TOKEN	The vault token to use for authentication
VAULT_CACERT	The path to the CA certificate to use for TLS verification
VAULT_CAPATH	The path to a directory of CA certificates to use for TLS verification
VAULT_CLIENT_CERT	The path to the client certificate to use for TLS connection
VAULT_CLIENT_KEY	The path to the client key to use for TLS connection