Managing Configuration Patterns

1. Externalized Configuration Pattern

Source	Use
Env Variables	12-factor; per-deploy overrides
Config Files	Mounted ConfigMaps / files
Config Server	Spring Cloud Config, etcd, Consul KV
Cloud Param Store	SSM Parameter Store, GCP Runtime Config
Never	Hardcode env-specific values

Capability	Detail
Central Store	Versioned config repo (often git-backed)
Environment Profiles	dev / stage / prod overlays
Refresh	Push (webhook) or pull (poll) updates
Encryption	Encrypt secret values at rest
Tools	Spring Cloud Config, Consul, etcd, AWS AppConfig

Aspect	Detail
Definition	Boilerplate / scaffold for new services (build, CI/CD, observability)
Tools	Backstage software templates, Cookiecutter, Yeoman
Benefits	Consistency, faster onboarding, golden path

Practice	Detail
Git-Backed	Config in version control; PR review
Pinned Versions	Service references config commit/tag
Rollback	Revert config without redeploy
Audit	Who changed what, when

Toggle Type	Lifespan
Release Toggles	Days/weeks; hide unfinished work in trunk
Experiment Toggles	Hours/days; A/B testing
Ops Toggles	Long-lived; kill switches
Permission Toggles	Permanent; per-user / per-tenant features
Tools	LaunchDarkly, Unleash, Flagsmith, ConfigCat

if (flags.isEnabled("new-checkout-flow", userContext)) {
    return newCheckoutService.process(req);
}
return legacyCheckoutService.process(req);

Aspect	Detail
Definition	Config changes apply without restart
Implementation	Watch config source; hot-reload listeners
Validation	Validate before applying; rollback on error
Use Cases	Log levels, rate limits, feature flags, tunables

Approach	Detail
Profile-Based	`application-{profile}.yaml` overlay
Per-Env Branches	GitOps with env-specific config
Helm Values	Per-env values.yaml
Avoid	If/else branching on env in code

Pattern	Detail
External Vault	Vault, KMS-backed
Sidecar Injection	Vault Agent injects to pod filesystem
CSI Driver	Mount secrets as files (K8s Secrets Store CSI)
Sealed/Encrypted	Sealed Secrets, SOPS for git storage

When	Detail
At Startup	Fail fast if invalid; refuse to start
At PR Time	Schema validation in CI
At Apply Time	Dry-run before live
Schemas	JSON Schema, Spring `@ConfigurationProperties` + JSR-303