⚙️ Environment Variables Configuration

Template for configuring your application settings

What Are Environment Variables?

Environment variables are settings that change depending on where the application runs.

Local Development:
FLASK_ENV=development

Production Server:
FLASK_ENV=production

Same code, different settings.

Why Use Environment Variables?

Without Environment Variables (Bad)

# In code (NEVER DO THIS!)
SECRET_KEY = "my-super-secret-key-12345"
DATABASE_URL = "postgresql://user:password@localhost/mydb"
DEBUG_MODE = True

Problems: - Secrets are visible in code - Can't change settings without editing code - Secrets get saved to git history - Everyone can see passwords

With Environment Variables (Good)

# In shell or platform config (DO THIS)
export SECRET_KEY="my-super-secret-key-12345"
export DATABASE_URL="postgresql://user:password@localhost/mydb"
export FLASK_ENV="production"

# In code (secure)
import os
SECRET_KEY = os.environ.get('SECRET_KEY')
DATABASE_URL = os.environ.get('DATABASE_URL')
FLASK_ENV = os.environ.get('FLASK_ENV', 'development')

Benefits: - Secrets are kept separate from code - Easy to change settings - Secrets are not in git history - Different settings per environment

Setting Environment Variables

Method 1: Command Line (Temporary)

# Set for one command
export FLASK_ENV=development
python run_v2.py

# Or in one line
FLASK_ENV=development python run_v2.py

# On Windows PowerShell
$env:FLASK_ENV="development"
python run_v2.py

How long it lasts: Until you close the terminal

Method 2: .env File (Local Development)

Create a file called .env in your project root:

# .env file
FLASK_ENV=development
FLASK_DEBUG=1
DATABASE_PATH=./core_v2/db_v2/app.db
SECRET_KEY=dev-key-not-for-production
PORT=5000
TIMEZONE=UTC

Then load it:

# In Python code or shell config
from dotenv import load_dotenv
load_dotenv()

How long it lasts: As long as your application runs

Method 3: Platform Dashboard (Production)

Most platforms (DigitalOcean, Heroku, AWS) have a dashboard:

Settings → Environment Variables
FLASK_ENV: production
SECRET_KEY: [your-production-key]
DATABASE_URL: [your-database-url]

How long it lasts: Until you change it

Method 4: Configuration Files (Advanced)

For complex setups, use configuration files:

# config.py
import os

class Config:
    SECRET_KEY = os.environ.get('SECRET_KEY') or 'dev-key'
    FLASK_ENV = os.environ.get('FLASK_ENV', 'development')

class DevelopmentConfig(Config):
    FLASK_DEBUG = True
    DATABASE_URL = 'sqlite:///dev.db'

class ProductionConfig(Config):
    FLASK_DEBUG = False
    DATABASE_URL = os.environ.get('DATABASE_URL')

config = {
    'development': DevelopmentConfig,
    'production': ProductionConfig,
    'default': DevelopmentConfig
}

Common Environment Variables

Application Settings

Database Settings

Security Settings

Application Settings

Logging & Monitoring

Configuration Templates

Local Development (.env)

# Flask Configuration
FLASK_ENV=development
FLASK_DEBUG=1
PORT=5000
HOST=localhost

# Database
DATABASE_PATH=./core_v2/db_v2/app.db

# Security
SECRET_KEY=dev-key-change-in-production

# Logging
LOG_LEVEL=DEBUG

Production (via Platform Dashboard)

FLASK_ENV=production
FLASK_DEBUG=0
PORT=8080
HOST=0.0.0.0

DATABASE_URL=postgresql://user:secure_password@db.example.com:5432/myapp

SECRET_KEY=[generate-random-key-here]

LOG_LEVEL=INFO
SENTRY_DSN=[sentry-error-tracking-url]

Testing (.env.test)

FLASK_ENV=testing
FLASK_DEBUG=1
DATABASE_PATH=./test.db
DATABASE_RESET=true

SECRET_KEY=test-key-not-secure

Reading Environment Variables in Code

Python

import os

# Get with default value
env = os.environ.get('FLASK_ENV', 'development')
port = int(os.environ.get('PORT', 5000))

# Get without default (will be None if not set)
secret = os.environ.get('SECRET_KEY')

# Require environment variable (error if missing)
api_key = os.environ['API_KEY']  # Raises KeyError if not set

Flask

from flask import Flask

app = Flask(__name__)
app.config['SECRET_KEY'] = os.environ.get('SECRET_KEY')
app.config['DATABASE_URL'] = os.environ.get('DATABASE_URL')

Generating Secure Keys

Secret Key (For Sessions)

# Python
python -c "import secrets; print(secrets.token_hex(32))"

# Result: 7f8c9d2e4a1b5c6f9e2d3a4b5c6f7e8d9a0b1c2d3e4f5a6b7c8d9e0f1a2b3c

# Use this as SECRET_KEY

API Keys

# Generate random API key
python -c "import uuid; print(str(uuid.uuid4()))"

# Result: a1b2c3d4-e5f6-7a8b-9c0d-1e2f3a4b5c6d

Security Best Practices

✅ DO - Store secrets in environment variables - Generate strong, random keys - Use different keys for each environment - Rotate keys regularly - Document which variables are required - Never commit .env files to git

❌ DON'T - Put secrets in code - Use simple/easy-to-guess values - Reuse keys across environments - Commit .env files - Share keys via email - Log sensitive values

.gitignore for Secrets

Make sure .env files are not committed:

# .gitignore
.env
.env.local
.env.*.local
__pycache__/
*.pyc
venv/

Checking Current Configuration

View Set Variables

# See all environment variables
env

# See specific variable
echo $FLASK_ENV  # Mac/Linux
echo %FLASK_ENV%  # Windows

# Python
import os
print(os.environ.get('FLASK_ENV'))

Verify Configuration

# In your application
@app.route('/config')
def config():
    return {
        'FLASK_ENV': app.config.get('FLASK_ENV'),
        'DEBUG': app.config.get('DEBUG'),
        'DATABASE': 'configured' if app.config.get('DATABASE_URL') else 'missing'
    }

Troubleshooting

"Environment variable not found"

Meaning: Variable isn't set

Solution:

# Set it first
export VARIABLE_NAME="value"

# Then run app
python run_v2.py

"Connection refused" (Database)

Meaning: DATABASE_URL is wrong or database isn't running

Solution:

# Check DATABASE_URL
echo $DATABASE_URL

# Verify database is running
# (platform/server specific)

"Module not found" in Production

Meaning: requirements.txt is incomplete

Solution:

# List all installed packages
pip freeze > requirements.txt

# Commit and deploy

Next Steps

• Set up your local .env file
• Configure environment variables on your deployment platform
• Generate secure keys for production

Key Takeaway: Environment variables keep secrets safe and let you use different settings for different environments without changing code.