Docker Compose — Compose Environment Variables
Learn every way to configure environment variables in Docker Compose — from inline definitions to .env files and variable substitution.
What You Will Learn
| # | Topic | Description |
|---|---|---|
| 1 | Environment Key | Inline environment variables |
| 2 | Env File Directive | Loading variables from files |
| 3 | Dotenv File | The magic .env file |
| 4 | Variable Substitution | Using variables in compose.yml |
| 5 | Secrets | Managing sensitive data |
| 6 | Practice Exercises | Hands-on challenges |
The Big Picture
┌─────────────────────────────────────────────────┐
│ Docker Compose │
│ │
│ .env file ──▶ Variable Substitution │
│ in compose.yml │
│ │
│ environment: ──▶ Container ENV vars │
│ env_file: ──▶ Container ENV vars (from file) │
│ secrets: ──▶ Mounted as /run/secrets/<name> │
└─────────────────────────────────────────────────┘
Understanding the difference between Compose-level variables (.env + substitution) and container-level variables (environment: / env_file:) is the key to mastering this chapter.
