Configuration, properties, and profiles

Code should describe behavior. Configuration should describe what changes between environments.

Typed properties

Use @ConfigurationProperties for a group of related settings. Typed objects provide validation, metadata, and one place to understand configuration. Prefer them over many scattered @Value expressions.

@ConfigurationProperties("payments")
public record PaymentProperties(
    @NotBlank URI endpoint,
    @Positive Duration timeout) {}

Property precedence

Spring Boot combines files, environment variables, system properties, command line arguments, test properties, and other sources with a defined precedence. Know which source wins. Do not let an emergency command-line override become an invisible permanent configuration.

Profiles

Profiles activate groups of beans or properties. Use them sparingly for genuine environment capabilities. Avoid profile combinations such as prod-eu-blue-customer7; they create untestable configuration branches.

Secrets

Do not store passwords or tokens in source control. Retrieve them from a secret manager or injected runtime source. Ensure logs and Actuator endpoints do not expose them. Plan rotation and application reload.

Validation and failure

Validate required configuration at startup with clear messages. A service that starts with a blank payment endpoint is not “resilient”; it is misleading.

Feynman check

Configuration is a labeled control panel. Typed properties group related switches, validation stops impossible settings, and a secret manager keeps the master key away from the panel.