Securing Container Images: Best Practices for a Robust Containerised Environment

Throughout 2024, my blog posts will primarily draw upon my security engineering and architecture experience, sharing the best practices I’ve implemented and the challenges I’ve conquered in AWS over the past decade.

In this month’s dive, I’m heading into the intricate world of container security, aiming to shed some much-needed light on the best ways to fortify your containerised infrastructure.

The three core pillars I consistently lean on when dealing with container images – principles I’ve successfully implemented in both financial and government departments – are: Image Scanning, Immutable Infrastructure, and Signing with Verification.

Pillar One – Image Scanning: Unveiling Vulnerabilities Before Deployment

As the old adage goes, “prevention is better than cure,” and that sentiment rings profoundly true for container security. It’s simply non-negotiable to utilise container image scanning tools to proactively sniff out vulnerabilities and security nasties within your images before they ever get deployed into production, or even released into public repositories. These intelligent tools meticulously analyse the very DNA of your images, meticulously checking for known vulnerabilities, outdated packages, and any potential threats lurking within.

By seamlessly integrating these scanning capabilities directly into your CI/CD pipelines – a practice often termed “shifting left” – you can effectively prevent security issues from ever making it to your live environments, ensuring a far more secure and compliant deployment. So, what fantastic tools are out there for this crucial scanning?

AWS Cloud-Native Tools for Image Scanning

Amazon ECR Image Scanning

Amazon Elastic Container Registry (ECR) offers a brilliant, built-in image scanning feature that automatically checks container images for vulnerabilities. Behind the scenes, it smartly leverages vulnerability intelligence from Snyk. You’ll find seamless integration with Common Vulnerabilities and Exposures (CVE) databases, automatic scanning whenever an image is pushed to ECR, and all findings neatly reported in AWS Security Hub for truly centralised visibility. It just works.

Amazon Inspector

While primarily focused on EC2 instances, Amazon Inspector can also be incredibly useful for container security. It provides comprehensive assessments of your running containers, flagging vulnerabilities and deviations from established security best practices. Plus, it integrates effortlessly with AWS Security Hub for those comprehensive security insights we all need.

Third-Party Image Scanning Tools

Clair

An excellent open-source container vulnerability scanner designed for analysing the security posture of your containers. Clair enables static analysis of container layers for vulnerabilities and offers smooth integration with popular container orchestration platforms like Kubernetes.

Aqua Security

Aqua provides a truly comprehensive security platform with a laser focus on securing containerised applications. It boasts robust image scanning capabilities for vulnerabilities and malware, alongside powerful runtime protection for your active containers.

Twistlock (Now part of Palo Alto Networks Prisma Cloud)

This is a robust cloud-native security platform delivering top-tier container security and compliance. It offers continuous scanning of container images and provides firm guard rails with policy enforcement for runtime security.

Pillar Two – Immutable Infrastructure: Build It Once, Trust It Forever

Embrace the powerful concept of immutable infrastructure, where your container images remain utterly unchanged throughout their entire lifecycle. Immutable infrastructure practices passionately advocate for treating infrastructure as code and deploying only immutable artifacts. This architectural philosophy inherently boosts security by drastically minimising the attack surface, significantly reducing the headache of configuration drift, and gloriously simplifying rollbacks.

At its very core, Immutable Infrastructure boldly challenges the traditional approach to infrastructure management. It champions the idea that infrastructure configurations are written like code, and only immutable artifacts – once created, never altered – are deployed. The term “immutable” perfectly captures the unchangeable nature of these deployed elements, ensuring that once an artifact is created, it stands firm and constant throughout its entire operational life.

Key Principles of Immutable Infrastructure

Infrastructure as Code (IaC)

Treat your infrastructure configuration as code. This allows for rigorous version control, absolute consistency, and perfect reproducibility. It naturally slashes the risk of misconfigurations and genuinely enhances security by enforcing configuration standards directly through your codebase.

Immutable Artifacts

Deploy only immutable artifacts, such as your container images, which remain untouched from their creation to their deployment. This fundamentally minimises the attack surface by eliminating any possibility of unauthorised changes or insidious tampering during runtime.

Rollback Simplicity

Imagine the ease of reverting to a previous, known-good artifact should any issues arise. This drastically simplifies rollback procedures, enabling lightning-fast responses to security incidents by allowing you to instantly revert to a secure, verified state without grappling with pesky configuration drift.

Applying Immutable Infrastructure to Container Images

In the bustling world of containerised environments, Immutable Infrastructure transforms how we manage images. Here’s how it powerfully contributes to both security and consistency:

By deploying only immutable container images, the attack surface is dramatically minimised because there are simply no runtime modifications possible, directly reducing the risk of hidden vulnerabilities.

Immutable container images provide absolute assurance that the image meticulously tested and approved in development is precisely identical to the one deployed in production, fostering unparalleled consistency and predictability.

Immutability inherently supercharges security by eradicating the need for runtime modifications, thereby slashing the potential for insidious security vulnerabilities to creep in.

While Immutable Infrastructure offers a treasure trove of advantages, it’s wise to consider the challenges, such as expertly managing stateful components and deftly handling dynamic configurations. Balancing these benefits with the specific, nuanced requirements of your applications is the real key to successful implementation.

Pillar Three – Signing and Verification: Safeguarding Authenticity and Integrity

Implementing image signing and verification mechanisms is often the one area many organisations struggle with, or regrettably, fail to implement at all. Yet, it is absolutely paramount to safeguard the authenticity and integrity of your container images. Image signing involves cryptographically signing your container images with a private key, while the subsequent verification uses the corresponding public key to ensure that the signature is valid and untampered. This meticulous process guarantees that the image you’re deploying hasn’t been meddled with or compromised during its journey.

Signing and verification form an exceptionally powerful duo in container security, providing a robust, often underestimated, layer of protection against unauthorised modifications or malicious alterations. These practices go well beyond mere image delivery, instilling a deep sense of trust in the true origin of your container images and profoundly mitigating the risks associated with deploying compromised or tampered containers.

This is especially critical when images are being produced for use by third parties, perhaps for software distribution. It provides the absolute assurance and trust that the image meticulously generated by the developer is precisely the image being used in the customer’s environment, utterly free from tampering.

Understanding Image Signing and Verification

Image Signing

Image signing involves cryptographically signing container images using a private key, which generates a unique signature for each image. This signature acts as a tamper-evident seal, providing clear evidence that the image originated from a trusted source and has not been subtly altered during its transit.

Verification Process

The verification process then employs the corresponding public key to scrupulously ensure the signature on the container image is valid. Validating this signature provides an unshakeable guarantee of the image’s authenticity and integrity, confirming unequivocally that it has not been compromised or tampered with in any way.

Safeguarding Container Images Through Signing and Verification

Trust in Image Origin: By signing container images, you establish a clear and verifiable chain of trust, empowering users and systems alike to confidently verify the image’s origin and absolute authenticity.

Integrity Assurance: Image verification ensures that the deployed container is an exact match for the signed version, brilliantly mitigating the risk of deploying maliciously tampered or otherwise compromised images.

Implementing signing and verification demonstrably elevates your overall security posture, furnishing a supremely reliable mechanism to actively counter potential security threats.

Tools and Technologies for Image Signing

Docker Content Trust (DCT)

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

Cosign

An excellent open-source project specifically designed for signing and verifying container images. Cosign offers effortless integration with existing CI/CD pipelines and supports multiple signature formats, making it wonderfully versatile.

Best Practices and Considerations

Effective key management is, of course, utterly crucial. You must safeguard private keys with the highest level of security and ensure the secure, trusted distribution of public keys. Furthermore, integrate signing and verification seamlessly into your CI/CD pipelines to automate the entire process and guarantee consistent, rigorous security checks without manual overhead.

Image signing and verification truly emerge as a definitive shield in the complex world of container security, ensuring that the containers you deploy are authentic, untampered, and, above all, secure. As you expertly navigate the intricate nuances of containerised environments, do actively consider implementing these practices to fortify your security posture and forge a truly resilient defence against potential threats.

In the next blog post, I’ll be diving deep into Identity and Access Management roles for ECS/EKS Tasks. We’ll explore how you can meticulously follow the principle of least privilege and help you really grasp the difference between Task Roles and Service Roles.

Until then, keep your head in the clouds.