Environment variables and secret managers are both used to keep credentials outside source code. They solve different parts of the problem. Environment variables are a delivery mechanism. A secret manager is a lifecycle and access-control system.
Why environment variables are popular
Applications can read environment variables without embedding credentials in code. They work across many frameworks, container systems, and deployment platforms. For small applications, this is a significant improvement over hard-coded secrets.
Environment variables can still leak
Process inspection, crash dumps, debugging tools, support bundles, shell history, deployment scripts, and accidental logging may expose environment values. The exact risk depends on the operating system and runtime.
What a secret manager adds
A dedicated manager can centralize storage, restrict access by identity, record retrieval, rotate values, issue dynamic credentials, and integrate with cloud or orchestration systems. Applications can retrieve secrets when needed instead of distributing static values widely.
Use the two together carefully
Some deployment systems retrieve a value from a secret manager and expose it to the application as an environment variable. This still improves centralized management, but the final process environment remains part of the threat model.
Choose based on risk and complexity
A small internal application may reasonably use protected environment configuration with strong server access controls. A production platform with many services, teams, and privileged credentials benefits more from centralized secret lifecycle management.
Do not forget rotation
Whatever storage method you choose, credentials need ownership and a rotation path. A securely stored secret that never changes can still become a long-term liability after personnel changes or suspected compromise.