Configuration: profiles, properties, and secrets

One binary, many environments

A Spring Boot app should build once and deploy everywhere. Environment-specific behavior — database URLs, credentials, feature flags — lives outside the jar, in properties, environment variables, or a secret store. Profiles select the right file for each environment.

# application.properties — safe defaults for local dev
app.feature.newCheckout=false
spring.datasource.url=jdbc:h2:mem:app

# application-prod.properties — overridden in prod profile
app.feature.newCheckout=true

Precedence (highest to lowest): command-line args, OS environment variables, application-{profile}.properties, application.properties, defaults in code. Use @ConfigurationProperties to bind properties to typed, validated POJOs.