Docker Environment Variables

Environment variables in Docker allow you to configure applications dynamically without changing the code. They are widely used for storing configuration such as database credentials, API keys, and environment settings.

Why Use Environment Variables?

• Keep sensitive data like passwords outside the code.
• Easily change configuration without rebuilding images.
• Support multiple environments (development, staging, production).

Set Environment Variables Using docker run

docker run -d 
  --name my-app 
  -e APP_ENV=production 
  -e DB_HOST=localhost 
  -e DB_USER=root 
  nginx

Using .env File

Create a .env file:

APP_ENV=production
DB_HOST=mysql
DB_USER=root
DB_PASSWORD=secret

Run container with env file:

docker run --env-file .env nginx

Environment Variables in Dockerfile

FROM ubuntu:22.04

ENV APP_NAME=OnlineLearner
ENV APP_ENV=production

CMD ["bash"]

Environment Variables in Docker Compose

version: "3.9"

services:
  app:
    image: my-app
    environment:
      APP_ENV: production
      DB_HOST: mysql
      DB_USER: root
      DB_PASSWORD: secret

Access Environment Variables in App

Example in PHP:

$env = getenv("APP_ENV");
echo $env;

Best Practices

• Do not store sensitive data directly in Dockerfile.
• Use .env files or secret managers.
• Keep environment-specific configs separate.

Summary

• Environment variables help configure apps dynamically.
• Use -e flag, .env files, or Docker Compose.
• Best for managing secrets and environment-based configs.