What is the difference between storing secrets in docker-compose files and injecting them at runtime from a secrets manager?

Why This Matters for Security Teams

The difference is not just where a credential lives, but how much blast radius it creates when that file is copied, committed, cached, or shared. A secret in a docker-compose file becomes a durable artefact that can leak through Git history, CI logs, local developer machines, and backup systems. Runtime injection keeps the secret outside the repository and makes access a controlled operational event, which is easier to log, rotate, and revoke. That aligns with the intent of the NIST Cybersecurity Framework 2.0, especially around governance, access control, and protection of sensitive data.

Practitioners often underestimate how quickly a convenience choice becomes an identity control problem. Once a shared compose file contains an API key, database password, or signing token, that value is no longer just configuration. It is a reusable credential with an uncertain lifecycle. In non-human identity terms, the workload or container is effectively operating with standing privilege unless the secret is issued, scoped, and monitored like any other identity.

In practice, many security teams encounter secret exposure only after a repository copy, incident review, or credential rotation has already created operational friction, rather than through intentional design.

How It Works in Practice

With docker-compose, a secret can be supplied in multiple ways, but the security outcome depends on whether it is committed into the file, loaded from the environment, or mounted from an external store. Storing the value directly in the compose file is the weakest pattern because it turns the secret into source text. Injecting at runtime shifts responsibility to the platform, orchestration layer, or secret manager, where policy can be applied consistently.

That model is stronger when the secret manager handles retrieval just before use, applies access policy, and records audit events. It also supports short-lived credentials, which reduces the value of a stolen secret. For containerised workloads, this is closer to the intent of the OWASP Non-Human Identity Top 10, which treats machine credentials as identities that need lifecycle control, not static configuration.

• Store only non-sensitive configuration in compose files.
• Fetch secrets at startup or mount them from a managed secret store.
• Use least-privilege access so each service gets only the credential it needs.
• Rotate secrets centrally and invalidate old values quickly.
• Log retrieval, access, and failed lookups for detection and review.

Where teams need stronger isolation, the best practice is to bind secrets to workload identity rather than to a human-managed file. That reduces manual handling and supports revocation when the container, pipeline, or node is no longer trusted. These controls tend to break down in ad hoc development environments because local overrides, copied compose files, and undocumented environment variables bypass the secret manager.

Common Variations and Edge Cases

Tighter secret handling often increases setup complexity, requiring organisations to balance developer convenience against reduced exposure. In small test environments, teams sometimes accept less stringent handling because the operational overhead of a full secrets platform outweighs the immediate risk. That tradeoff is real, but current guidance suggests the exception should be explicit and temporary, not the default for production-like systems.

There is also no universal standard for this yet across every container platform. Some teams rely on environment variables, others on mounted files, and others on orchestration-native secret objects. The main security question is whether the secret is persisted in a recoverable place outside the intended trust boundary. If it is, rotation and revocation remain harder than they should be.

Edge cases appear when debugging tools, image layers, CI variables, or crash dumps retain the injected value after deployment. Runtime injection is better, but only if the secret is not echoed into logs or baked into a derived image. For regulated or high-trust environments, the operational benchmark should be whether the secret can be traced, rotated, and removed without touching source control or rebuilding every dependent service.

Related resources from NHI Mgmt Group

• What is the difference between runtime protection and NHI lifecycle management?
• What is the difference between storing secrets securely and governing them well?
• What is the difference between rotating a secret and revoking access?
• What is the difference between rotation and deprovisioning for NHIs?