Secrets in Kubernetes

Managing sensitive data like passwords, API keys, and SSL certificates is a key challenge when building applications on Kubernetes. Secrets provide a resource type in Kubernetes specifically for storing confidential data safely. With secrets, you can keep sensitive values out of your application source code and control access to them through RBAC policies.

There are a few primary ways to use secrets in Kubernetes:

First, you can create secret objects containing key-value data like passwords or tokens. This secret data can be defined directly on the command line, in a manifest file, or generated from file contents. The data is encoded in base64 when stored in etcd to prevent accidental exposure through logs.

Next, pods can consume secrets by having them mounted as volumes or exposed as environment variables. This allows your application code to access secrets without hardcoding confidential data. For example, a pod might mount a secret containing an SSL certificate to use for HTTPS.

Secrets open up more advanced options as well, like pulling container images from private registries or dynamically generating secrets from external providers. Overall, secrets are a powerful tool for managing sensitive data in a Kubernetes environment.

With some best practices like encryption, backup, and rotation, you can build robust secret management using Kubernetes primitives. This introduction covers the basics of how secrets work and their main use cases in Kubernetes workflows.

Why Use Secrets?

Secrets keep confidential data out of your application's source code. This prevents accidental commits of passwords or keys to source control.  Secrets can be mounted as environment variables or volumes for use by pods, without exposing the secret values directly in pod definitions.  The Kubernetes API authenticates and authorizes requests to access secret data. This prevents unauthorized users from accessing secret values.

Creating Secrets

You can create secrets in a few different ways:

kubectl: Use kubectl create secret and specify secret data on the command line:

kubectl create secret generic db-password --from-literal=password=mysqlpassword        

Manifest file: Create a secret manifest YAML file containing the secret data encoded in base64:

apiVersion: v1
kind: Secret
metadata:
  name: db-password
type: Opaque
data:
  password: bXlzcWxwYXNzd29yZA== # base64 encoded password        

Generate file: Use kubectl create secret generic and point to files containing the secret data:

kubectl create secret generic ssl --from-file=privatekey=~/certs/private.key --from-file=certificate=~/certs/public.crt        

Secrets created from files encode the file contents in base64 automatically.

Using Secrets

There are a few primary ways pods can consume secrets:

Environment variables: Set secret data as the value for environment variables in a pod spec:

env:
  - name: DB_PASSWORD
    valueFrom:
      secretKeyRef:
        name: db-password
        key: password        

Volume mounts: Mount secrets as files in a volume mounted on one or more containers:

volumes:
  - name: db-password-vol
    secret:
      secretName: db-password
containers:
  - name: db
    volumeMounts:
      - name: db-password-vol
        mountPath: "/etc/secrets"
        readOnly: true        

Image pulls: Use a secret to store credentials for accessing private container registries:

imagePullSecrets:
- name: regcred        

This covers the basics of working with secrets in Kubernetes. Secrets allow you to safely store and manage access to sensitive data.

Advanced Uses of Secrets

In addition to the basic ways to create and consume secrets, there are some more advanced secret usage patterns.

Dynamic Secrets

Secrets can be generated dynamically instead of creating them from static files. For example:

• Use an init container to generate a secret file from a database credential store.
• Call a vault API from an init container to retrieve a temporary credential to use as a secret.
• Use a Kubernetes controller to watch an external secret store and automatically create secrets.

Dynamic secret generation allows integrating Kubernetes with other security systems.

Encrypting Secrets

By default, secret data is base64 encoded but not encrypted. Anyone with API access can retrieve the secret values.

To encrypt secret data at rest:

• Enable encryption providers like aescbc or kms plugin on the Kubernetes cluster.
• Create secrets with type kubernetes.io/tls to encrypt them.

This protects secret data if the API is compromised.

Injecting Secrets with a Sidecar

Instead of mounting secrets to main app containers, inject them via a sidecar. The sidecar watches for changes and provides secrets to the main app.

Benefits:

• Main app does not need access to the Kubernetes API.
• Secret injection can be customized by the sidecar.

This increases separation between apps and infrastructure.

Backup and Rotation

Have a process to periodically backup and rotate secret values, especially for signing keys and passwords.

Otherwise secrets can be lost if nodes fail or keys are compromised. Backup secrets externally or have a rotation schedule.

Conclusion

Secrets provide a flexible way to manage sensitive data like credentials, keys, and certificates in your Kubernetes clusters. By using secrets, you can prevent confidential data from being exposed in your application code or pod definitions.

Some key takeaways are that secrets allow you to decouple storage and management of sensitive data from your application logic. Kubernetes provides native APIs for creating secrets from files, literals, or external sources and controlling access through RBAC. Pods can consume secret data through environment variables or mounted volumes without having direct access.

For production deployments, enable encryption providers to encrypt secret data at rest. Have automated processes for periodically backing up and rotating secrets to prevent data loss. You can also use patterns like sidecar containers to customize how secrets are injected.

Overall, secrets give you granular control over sensitive data and integration with Kubernetes workflows. Make use of them as part of your security best practices. Ensure proper RBAC policies, encryption, backup processes, and rotation schedules are in place. With some forethought, secrets can help securely manage credentials, keys, certificates and other critical data in your Kubernetes clusters.