Containerization and Kubernetes have transformed application deployment, but they introduce security challenges requiring specialized approaches. Securing containerized environments demands attention across multiple layers from images to orchestration.
Image Security Fundamentals
Container images form the foundation of containerized applications. Start with minimal base images containing only necessary components. Official images from trusted registries reduce supply chain risks, but even these require verification and regular updates.
Scan images for vulnerabilities before deployment using tools that check for known CVEs in packages and dependencies. Integrate scanning into CI/CD pipelines to catch issues before they reach production. However, scanning alone isn’t sufficient—remediation processes must address discovered vulnerabilities promptly.
Never include secrets like passwords, API keys, or certificates directly in images. Secrets baked into images persist in all layers, remaining accessible even when deleted. Use secret management systems to inject credentials at runtime instead.
Runtime Security
Containers should run as non-root users whenever possible. While containers provide isolation, running as root unnecessarily expands attack surface if containment fails. Define USER directives in Dockerfiles to specify non-privileged users for application processes.
Implement read-only root filesystems for containers that don’t require write access. This prevents attackers from modifying binaries or installing additional tools within compromised containers. Mount specific directories as writable when applications legitimately need write access.
Resource limits prevent individual containers from monopolizing cluster resources, whether through bugs or malicious activity. Set CPU and memory constraints appropriately based on application needs to maintain availability during resource exhaustion attacks.
Kubernetes Security Posture
Role-Based Access Control (RBAC) in Kubernetes requires careful configuration. Follow least privilege principles when assigning permissions to service accounts. Default service accounts should have minimal permissions, with specific accounts created for applications requiring elevated access.
Network policies provide microsegmentation within clusters, controlling which pods can communicate with each other. Default-deny policies combined with specific allow rules limit lateral movement opportunities for attackers who compromise individual containers.
Pod Security Standards enforce security configurations at the pod level. Baseline standards prevent obviously risky configurations while restricted standards enforce hardened settings. Implement these standards through admission controllers that reject non-compliant pod specifications.
Secrets Management
Kubernetes Secrets provide basic secret storage, but they’re base64 encoded rather than encrypted by default. Enable encryption at rest for the etcd datastore where secrets are stored. Consider external secret management solutions that provide additional features like automatic rotation and audit logging.
Limit secret access through RBAC policies. Not all pods need access to all secrets. Bind secrets only to service accounts that require them, and use namespaces to create additional boundaries around sensitive credentials.
Admission Control
Admission controllers intercept requests to the Kubernetes API before objects are persisted, enabling policy enforcement. PodSecurityPolicy, though deprecated in favor of Pod Security Standards, demonstrates the concept of preventing insecure configurations from being deployed.
Custom admission controllers using ValidatingWebhookConfiguration and MutatingWebhookConfiguration enable organization-specific policies. These can enforce image pull policies, require specific labels, inject sidecars, or validate compliance with internal standards.
Monitoring and Logging
Comprehensive logging of API server activity, container runtime events, and application logs provides visibility into cluster operations. Centralized log aggregation enables correlation of events across multiple components to identify suspicious patterns.
Runtime threat detection tools analyze container behavior to identify anomalies like unexpected network connections, file access patterns, or process executions. These tools help detect compromises even when attacks use zero-day exploits that don’t appear in vulnerability databases.
Service Mesh Security
Service meshes like Istio provide transparent mutual TLS between services, encrypting internal communications without application code changes. They also enable fine-grained authorization policies controlling service-to-service communication based on identity rather than network location.
Service mesh observability features provide detailed metrics about communication patterns, helping identify abnormal behavior. However, service meshes add complexity and resource overhead, requiring careful consideration of tradeoffs for your environment.
Supply Chain Security
Image signing and verification ensures containers haven’t been tampered with between build and deployment. Tools like Notary and Cosign cryptographically sign images, with admission controllers verifying signatures before allowing deployment.
Maintain an inventory of all images in use across clusters. Know what software runs in your environment, including versions and dependencies. This enables rapid response when vulnerabilities are disclosed in popular packages or base images.
Cluster Hardening
Restrict access to the Kubernetes API server using network policies or firewall rules. Disable anonymous authentication and insecure port access. Enable audit logging to track all API interactions for security analysis and compliance.
Keep Kubernetes components updated with security patches. New vulnerabilities are regularly discovered in Kubernetes itself, requiring timely updates to maintain security. Test updates in non-production environments before applying to production clusters.
Conclusion
Container and Kubernetes security requires defense-in-depth across image creation, runtime configuration, cluster hardening, and ongoing monitoring. By implementing security best practices at each layer, organizations can safely leverage the benefits of containerized applications while managing associated risks.