As containerized applications become more prevalent, managing sensitive data such as passwords, API keys, and credentials — referred to as secrets — poses a significant security challenge. If not handled properly, secrets in containers can be exposed to unauthorized access, leading to data breaches or compromised applications.

In this blog, we’ll explore what secrets are in the context of containerization, the risks associated with improper management, and best practices for securely handling secrets in containers.

What Are Secrets in Containers?

Secrets are sensitive pieces of information that applications need to function correctly. These could include:

• Database credentials
• API keys
• SSH keys
• Encryption keys
• OAuth tokens

In a containerized environment, these secrets are essential for services to communicate and authenticate securely. However, embedding these secrets directly into the container image or code is dangerous, as it risks exposure to unauthorized users.

Risks of Mismanaging Secrets

Improper management of secrets can lead to several serious risks, including:

1. Exposed Secrets in Container Images: Storing secrets in container images is a common mistake. Since container images can be pushed to public registries or shared among teams, secrets stored this way are easily accessible.
2. Plaintext Secrets in Environment Variables: While it’s tempting to use environment variables to pass secrets to containers, they are not secure. Anyone with access to the running container can potentially read these variables.
3. Insecure Transmission: If secrets are not encrypted during transmission between services or containers, they can be intercepted by malicious actors.
4. Insufficient Access Control: Failing to restrict access to secrets can lead to unauthorized personnel or services accessing sensitive data.

Best Practices for Managing Secrets in Containers

To ensure your containerized applications are secure, it’s critical to follow best practices for secrets management. Here’s how you can safeguard sensitive information:

1. Use Secret Management Tools

Secret management tools are purpose-built to handle sensitive data securely. These tools allow you to store, access, and manage secrets without embedding them directly in container images or code. Some widely used secret management tools include:

• HashiCorp Vault: An open-source tool that allows secure storage, access control, and auditing of secrets.
• AWS Secrets Manager: Manages and retrieves secrets securely for applications running in the AWS cloud.
• Azure Key Vault: Provides secure storage of secrets in Microsoft Azure environments.
• Google Cloud Secret Manager: Manages secrets for applications running in Google Cloud.

These tools often integrate with container orchestration platforms like Kubernetes to inject secrets securely into containers at runtime.

2. Use Kubernetes Secrets

If you are using Kubernetes for container orchestration, you can leverage Kubernetes Secrets to manage sensitive information. Kubernetes allows you to store and manage secrets outside of container images in an encrypted format. You can define a secret and then mount it as a file or pass it as an environment variable within the container.

However, there are a few considerations to ensure Kubernetes Secrets are used securely:

• Enable encryption at rest: Ensure that Kubernetes secrets are encrypted at rest using encryption providers.
• Limit access to secrets: Use Role-Based Access Control (RBAC) policies to restrict who and what can access the secrets.
• Avoid environment variables: Although Kubernetes allows passing secrets via environment variables, it’s safer to mount secrets as files within containers.

3. Use Secrets as Mounted Volumes

Instead of passing secrets via environment variables, which are often insecure, you can mount secrets as volumes in the container. This approach is more secure because it reduces the risk of exposure if someone gains access to the running container’s environment.

For instance, Kubernetes supports mounting secrets as files. These files can then be read by the application at runtime.

4. Encrypt Secrets at Rest and In Transit

Whether secrets are stored in Kubernetes or managed via a third-party secret management tool, encryption is critical to protecting them. Ensure that:

• Secrets are encrypted at rest: Data at rest should always be encrypted to protect against data breaches, especially in cloud storage or container registries.
• Secrets are encrypted in transit: Use encryption protocols (like TLS/SSL) to secure data during transmission between services, containers, and external APIs.

5. Implement Least Privilege Access

Follow the principle of least privilege when granting access to secrets. Only authorized applications, services, and personnel should have access to the secrets required for their function. Use role-based access control (RBAC) and network policies to enforce strict access controls.

For example:

• Use Kubernetes RBAC to ensure only specific services or pods can access certain secrets.
• Limit secrets to specific namespaces, containers, or pods in Kubernetes.

6. Rotate Secrets Regularly

Regularly rotating secrets is crucial for limiting the damage in case a secret is compromised. Many secret management tools support automatic secret rotation, which helps ensure that credentials, API keys, and tokens are regularly updated without manual intervention.

In Kubernetes, you can update a secret without restarting your pods by using mounted volumes, which are automatically updated when the secret changes.

7. Audit and Monitor Secret Access

Monitoring access to secrets is critical for detecting potential security breaches. Most secret management tools and platforms like Kubernetes offer logging and audit trails that track who accessed a secret and when.

• Enable auditing in Kubernetes to log secret access attempts.
• Regularly review these logs to identify any unusual activity or unauthorized access.

8. Avoid Hardcoding Secrets

One of the biggest mistakes developers can make is hardcoding secrets directly into application code or configuration files. This practice significantly increases the risk of exposure, especially if the code is pushed to a public repository like GitHub.

Instead, use secret management tools to inject secrets at runtime, ensuring they are never hardcoded into the application itself.

9. Limit Secrets Lifecycle

Limit the lifecycle of your secrets by setting expiration times. This ensures that old secrets are invalidated after a certain period and reduces the attack surface if a secret is exposed.

Many secret management tools allow you to define TTL (time-to-live) values for secrets, automatically invalidating them after the defined period.

Conclusion

Managing secrets in containers is a critical component of application security. By following best practices like using secret management tools, encrypting secrets, limiting access, and rotating them regularly, you can reduce the risk of sensitive data exposure and protect your applications from breaches. As containers continue to power modern applications, the importance of secure secret management will only grow.