Securing Container Images

Securing Container Images: Best Practices for a Robust Containerized Environment

Throughout 2024 my blog posts will mainly draw upon my security engineering and architecture experience, sharing best practices I have used and how I have conquered challenges in AWS over the past 10+ years.

In this months post I’m diving into the intricate world of container security, shedding light on best practices to fortify your containerized infrastructure.

The three key pillars I follow with containerized images which I have implemented into financial and government departments are: Image Scanning, Immutable Infrastructure, and Signing with Verification.

Pillar One - Image Scanning: Unveiling Vulnerabilities Before Deployment

As the saying goes, “prevention is better than cure,” and the same holds true for container security. Utilise container image scanning tools to proactively identify vulnerabilities and security issues within your images BEFORE deploying them into production, or releasing them into public repositories. These tools meticulously analyse the contents of your images, checking for known vulnerabilities, outdated packages, and potential threats.

By integrating scanning into your CI/CD pipelines, shifting left, you can prevent security issues from reaching production, ensuring a more secure and compliant deployment. So what is available for scanning?

AWS Cloud-Native Tools for Image Scanning

Amazon ECR Image Scanning

Amazon Elastic Container Registry (ECR) provides a built-in image scanning feature that automatically scans container images for vulnerabilities, it utilises vulnerability intelligence from Snyk in the background. You have integration with Common Vulnerabilities and Exposures (CVE) databases, automatic scanning on image push to ECR with all of the findings reported in AWS Security Hub for centralized visibility.

Amazon Inspector

While primarily focused on EC2 instances, Amazon Inspector can also be used for container security. It provides assessments of running containers for vulnerabilities and deviations from security best practices. There is integration with AWS Security Hub for comprehensive security insights.

Third-Party Image Scanning Tools


An open-source container vulnerability scanner for analyzing the security of containers. This enables static analysis of container layers for vulnerabilities you can also integrate with container orchestration platforms like Kubernetes.

Aqua Security

A comprehensive security platform with a focus on securing containerized applications. It has image scanning for vulnerabilities and malware and also runtime protection for running containers.

Twistlock (Now part of Palo Alto Networks Prisma Cloud)

A cloud-native security platform providing container security and compliance. It provides continuous scanning of container images and guard rails with policy enforcement for runtime security.

Pillar Two - Immutable Infrastructure

Embrace the concept of immutable infrastructure, where container images remain unchanged throughout their lifecycle. Immutable infrastructure practices advocate treating infrastructure as code and deploying only immutable artifacts. This approach enhances security by minimizing the attack surface, reducing the risk of configuration drift, and simplifying rollbacks.

At its core, Immutable Infrastructure challenges the traditional approach to infrastructure management by advocating for treating infrastructure as code and deploying only immutable artifacts. The term “immutable” reflects the unchangeable nature of the deployed artifacts, ensuring that once an artifact is created, it remains unchanged throughout its lifecycle.

Key Principles of Immutable Infrastructure

Infrastructure as Code (IaC)

Treat infrastructure configuration as code, allowing for version control, consistency, and reproducibility. This reduces the risk of misconfigurations and enhances security by enforcing configuration standards through code.

Immutable Artifacts

Deploy only immutable artifacts, such as container images, which remain unchanged from creation to deployment. This minimizes the attack surface by eliminating the possibility of unauthorized changes or tampering during runtime.

Rollback Simplicity

Simplify rollback procedures by redeploying a previous, known-good artifact in case of issues. It enables quick response to security incidents by reverting to a secure state without dealing with configuration drift.

Applying Immutable Infrastructure to Container Images

In the context of containerized environments, Immutable Infrastructure transforms the way we approach image management. Here’s how it contributes to security and consistency:

By deploying only immutable container images, the attack surface is minimized as there are no runtime modifications, reducing the risk of vulnerabilities.

Immutable container images ensure that the image tested and approved in development is identical to the one deployed in production, fostering consistency and predictability.

Immutability inherently enhances security by eliminating the need for runtime modifications, reducing the potential for security vulnerabilities.

While Immutable Infrastructure offers numerous advantages, it’s essential to consider the challenges, such as managing stateful components and handling dynamic configurations. Balancing the benefits with the specific requirements of your applications is key to successful implementation.

Pillar Three - Signing and Verification: Safeguarding Authenticity and Integrity

Implement image signing and verification mechanisms is the one area most organisation struggle with and often don’t implement this. It is to safeguard the authenticity and integrity of your container images. Image signing involves cryptographically signing your container images with a private key, while verification uses the corresponding public key to ensure the signature is valid. This process guarantees that the image has not been tampered with or compromised during transit.

Signing and verification form a powerful duo in the realm of container security, providing a robust layer of protection against unauthorized modifications or malicious alterations. These practices go beyond simple image delivery, instilling trust in the origin of your container images and mitigating the risks associated with deploying compromised or tampered containers.

It is particularly important where images are being produced for use by third parties, like software distribution and provides the trust that the image generated by the developer is the image being used in the customers environment without tampering.

Understanding Image Signing and Verification

Image Signing

Image signing involves cryptographically signing container images with a private key, generating a unique signature for each image. The signature serves as a tamper-evident seal, ensuring that the image originated from a trusted source and has not been altered during transit.

Verification Process

The verification process employs the corresponding public key to ensure the signature on the container image is valid. Validating the signature guarantees the authenticity and integrity of the image, confirming that it has not been compromised or tampered with.

Safeguarding Container Images Through Signing and Verification

Trust in Image Origin, by signing container images, you establish a chain of trust, allowing users and systems to verify the image’s origin and authenticity. Image verification ensures that the deployed container matches the signed version, mitigating the risk of deploying tampered or compromised images. Implementing signing and verification elevates your overall security posture, providing a reliable mechanism to counter potential security threats.

Tools and Technologies for Image Signing

Docker Content Trust (DCT)

Integrated into Docker, DCT allows the signing and verification of images using the Docker Notary service. This enables content trust enforcement during image pulls and supports offline signing for enhanced security.


An open-source project for signing and verifying container images. Easy integration with existing CI/CD pipelines. Supports multiple signature formats.

Best Practices and Considerations

Effective key management is crucial. Safeguard private keys and ensure secure distribution of public keys. Integrate signing and verification seamlessly into your CI/CD pipelines to automate the process and ensure consistent security checks.

Image signing and verification emerge as a definitive shield in the realm of container security, ensuring that the containers you deploy are authentic, untampered, and secure. As you navigate the complexities of containerized environments, consider implementing these practices to fortify your security posture and build a resilient defense against potential threats.

In the next blog I will dive into Identity and Access Management roles for ECS/EKS Tasks, how you can follow the principle of least privilege and help understand the difference between Task Roles and Service Roles.

Until then, keep your head in the clouds.