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Container Images Explained

Take a deep dive into the world of container images and learn their essential role in cloud security.

6 minutes read

What is a container image?

A container image is a compact, self-contained software unit that encapsulates all the essentials required to execute a software application (such as the code, runtime environment, system utilities, libraries, and configurations). Unlike virtual machines, which require an entire guest operating system, container images share the host system's kernel but package the application and its dependencies into a containerized environment.

Container technology has revolutionized how developers deploy and manage applications in modern cloud environments, offering a level of portability and efficiency that was previously unimaginable. By encapsulating the application and its environment, developers can ensure that the software runs consistently and that there won’t be issues when it’s transferred between different computing environments. This portability is crucial in cloud ecosystems, where applications frequently move between local testing environments, staging environments, and production environments hosted on cloud platforms.

This blog post takes a deep dive into the world of container images and highlights their essential role in cloud security. First, let’s look at the parts of a container image before exploring how container images are stored, managed, and secured in container image registries.

How does container architecture work?

Container architecture consists of three foundational elements to create, store, and run containers:

Container images

A container image is composed of several container layers stacked upon each other, each representing a change or addition to the image. The first, foundational layer is a base image that includes the operating system and essential libraries. Additional writable layers are then added for application dependencies and libraries. The final application layer incorporates the actual source code, preparing the image for execution in any compatible runtime environment.

Container images are built from instructions specified in a Dockerfile. A Dockerfile is a text file that lists all the command-line instructions necessary for building an image. Using a Dockerfile, developers can define the base image, add files, execute commands, and set environment variables to create the container image. The build process executes the instructions in the Dockerfile sequentially, creating a new layer for each instruction that modifies the image:

Figure 1: Dockerfile to container image (Source: Docker)

The resulting container image can then be pushed to a container image registry, such as Docker Hub, making it available for others to pull and use.

Container images are immutable. Because they cannot be altered once built, there are significant advantages for cloud security. These benefits include maintaining consistency across deployments (reducing the "it works on my machine" problem) and easy rollbacks to stable versions without extensive troubleshooting. Immutability also enhances security by quickly replacing compromised containers with fresh, unaltered instances, swiftly mitigating potential attacks.

Container image registries

Container image registries are centralized repositories designed to store and distribute container images. Developers use these registries to push their container images and pull them for deployment. Docker Hub is the most well-known registry, home to an extensive collection of both public and private images. Similarly, cloud providers offer their own registries, such as AWS ECR and Google GCR, and these provide tight integration with their cloud services and security features.

An essential aspect of managing container images is tagging, which allows developers to specify versions of their images. Tags are labels attached to images that signify versions (e.g., 2.1, latest) or configurations (e.g., prod, test). The proper use of tags helps manage different versions of the same application and facilitates rollbacks to a previous version if needed.

Container runtimes

Container runtimes are the software components that run containers based on images. They are responsible for pulling the container image from a registry, unpacking it on the host, and running the application inside the container environment. 

The deployment of a container from an image involves several steps orchestrated by the container runtime:

Figure 2: Container image workflow (Source: Docker)

Container runtime environments come in various flavors, each with its own set of features and capabilities. The most well-known among them is Docker, which popularized container technology and made it accessible to developers worldwide. However, the landscape of container runtimes has evolved. Now, we have other significant players like containerd and CRI-O, which cater to different needs and integrate tightly with Kubernetes, the de-facto standard for orchestrating containerized applications.

The importance of container images

Container images are more than just a trend; they are a fundamental shift in how we deploy and manage applications in the cloud. Their importance lies in the myriad benefits they bring to the deployment process:

  • Speed and efficiency in deployment processes: One of the most significant advantages of container images is their speed and efficiency. Since container images encapsulate an application and all its dependencies, developers can spend less time setting up environments and more time coding, testing, and deploying, which accelerates the development life cycle.

  • Consistency across different environments: Container images guarantee consistent runtime, no matter the deployment location. This consistency reduces bugs and issues that arise from discrepancies across environments, making it easier to manage and update applications.

  • Scalability and microservices architecture support: Container images naturally support scalability and microservices architecture, enabling applications to be divided into smaller, autonomous units for independent deployment and scaling. This scalability is essential for modern applications to swiftly adapt to fluctuating demands and performance needs.

  • The role of container images in cloud security: Beyond deployment efficiency and scalability, container images play a crucial role in cloud security. Their immutable nature means that once an image is created, it cannot be altered, ensuring that the application environment remains consistent and tamper-proof across the deployment pipeline. Immutability, combined with the ability to scan images for vulnerabilities before deployment, enhances the security posture of applications in the cloud.

Security implications of container images

While container images bring numerous benefits, they also introduce specific container security considerations that organizations must address. Because vulnerabilities within images can be exploited when containers are run, the security of container images is paramount.

Common security risks for container images

  • Vulnerable dependencies: Container images often include third-party libraries and dependencies that may contain vulnerabilities. If not regularly updated, these can become security risks.

  • Misconfigurations: Incorrectly configured container images can expose applications to security threats like unauthorized access or data leakage.

  • Compromised images: If an attacker gains access to a container image registry, they could replace legitimate images with compromised ones, leading to the deployment of malicious containers.

  • Hardcoded secrets: Embedding hardcoded secrets (such as passwords or API keys) within container images can pose a significant risk. If the image is compromised, these secrets can be easily accessed by attackers, leading to further security breaches.

Best practices for securing your container images

Ensuring the security of container images involves adopting best practices throughout the image life cycle, from creation to deployment:

Source container images wisely and authenticate images

  • Ensure images are obtained from trusted sources.

  • Use official images from reputable registries and verify the authenticity of images.

  • Use image signing to verify the integrity and origin of container images. 

As we’ve seen, having trust in container images and the registries they’re pulled from is crucial. Organizations must ensure that the images they use are from reputable sources and have not been tampered with. Techniques such as image signing and verification can help establish trust by ensuring that an image has been created by a trusted source and has not been altered:

Figure 3: Signed image tags in a Docker registry (Source: Docker)

Regularly scan images for vulnerabilities

  • Implement automated scanning of images as part of the CI/CD pipeline to identify and remediate vulnerabilities before deployment.

  • Choose base images that include only the essential components needed for the application to run, minimizing potential vulnerabilities.

Manage secrets and sensitive data correctly

  • Do not store secrets or sensitive data directly in container images to prevent unauthorized access.

  • Employ secure secrets management tools and services to handle sensitive information outside of container images.

  • Ensure strict access controls for managing and accessing secrets, limiting them to only the components that require access.

Adopting these best practices can significantly enhance the security of container images and, by extension, the security of containerized applications in the cloud.

Wiz's approach to container image security

Looking for unmatched protection and compliance across AWS, Azure, Google Cloud, and Kubernetes? Wiz's agentless cloud security platform is designed to secure everything you build and run in the cloud, facilitating a collaborative environment where security, development, and DevOps teams can work together seamlessly. 

Wiz stands apart by providing a unified security platform that encompasses CNAPP, CSPM, container and Kubernetes security, vulnerability management, and data security—all aimed at reducing risk, enhancing visibility, and ensuring business agility. By integrating directly into development workflows, Wiz offers proactive vulnerability management, IaC and secrets scanning, and comprehensive workload protection so that every layer of your cloud environment (including containers!) is continuously monitored and protected against vulnerabilities, misconfigurations, and threats.

Container technologies are here to stay. And because containers play a critical role in cloud security, it’s essential to adopt advanced security solutions like Wiz. Wiz not only simplifies the process of securing your containerized applications but also empowers teams to maintain a robust security posture across all cloud environments. See for yourself by scheduling a demo today!

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