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Container Runtimes Explained

A container runtime is the foundational software that allows containers to operate within a host system.

5 minutes read

What is a container runtime?

A container runtime is the foundational software that allows containers to operate within a host system. Container runtime is responsible for everything from pulling container images from a container registry and managing their life cycle to running the containers on your system.

Here, we review the history of container runtimes, their role in modern software development, and how they compare to traditional virtual machines. We look at the layers of container runtimes, their importance in the DevOps pipeline, and important security implications.

Container runtimes: An in-depth look

Tracing its roots back to early Unix systems, container technology has evolved substantially over the years. Docker's launch in 2013 marked a pivotal moment, making containerization more accessible and spurring widespread adoption. In modern software development, containers are essential, providing lightweight, efficient, and consistent environments that address the "it works on my machine" problem by encapsulating applications and their dependencies.

Unlike virtual machines—which virtualize hardware and require a complete operating system for each instance—containers are more efficient, virtualizing at the OS level and sharing the host's kernel. This efficiency makes containers ideal for deploying microservices and achieving scalable, high-performance applications.

The more widely companies use containers, the more likely they are to call security their top challenge with containers.

Functionality and responsibilities

Understanding core functionalities and responsibilities is vital to appreciating how container runtimes facilitate the seamless execution and management of containers:

Execution of containers

Container runtimes primarily execute containers through a multi-step process. As a first step, this process begins by creating containers and initializing their environment based on a container image that contains the application and its dependencies. Following creation, the runtime runs the containers, starts the application, and ensures its proper function. Additionally, the runtime manages containers’ life cycles, which involves monitoring their health, restarting them if they fail, and cleaning up resources once the containers are no longer in use.

Interaction with the host operating system

Container runtimes interact closely with the host operating system. They leverage various features of the OS, like namespaces and cgroups, to isolate and manage resources for each container. This isolation guarantees that processes inside a container are unable to disrupt the host or other containers, preserving a secure and stable environment.

Resource allocation and management

Container runtimes are an essential part of resource management because they allocate and regulate CPU, memory, and I/O for each container to prevent resource monopolization, especially in multi-tenant environments. The way container runtimes smoothly handle the running, life cycle, and interaction of containers with the host OS is key to why containerization is such a big part of today's software development landscape.

Container runtimes vs. container engines

While a container runtime is responsible for running containers, a container engine is a broader system that manages even more of the life cycle of containers, including image distribution, container orchestration, and runtime management. 

One common misconception is that Docker and container runtimes are the same. While Docker Engine includes a container runtime, it also offers a suite of tools for building, shipping, and running containerized applications, making it much more than just a runtime.

Types of container runtimes

The landscape of container runtimes is diverse, designed to meet a wide range of requirements from essential container execution to complex orchestration needs. Container runtimes can be broadly classified into low-level runtimes, high-level runtimes, and specialized runtimes, each offering unique features and levels of abstraction:

DescriptionKey featuresResource managementInteraction with Linux kernel SecurityUse cases
Low-level container runtimesFundamental, minimal runtimes that interact directly with the OS kernel- Direct OS interaction - Efficient and fine-grained controlFine-grained control over resourcesDirect interaction with features like namespaces and cgroupsBasic, reliant on host OS security features- Scenarios requiring a lightweight, minimal tool for running containers - Used in larger systems where other tools handle orchestration
High-level container runtimesMore abstracted runtimes, offering additional functionalities beyond basic execution- Image management - Basic networking capabilities - User-friendly interfaceBroader management capabilities, often integrated with orchestration platformsAbstracted interaction, often through additional layers or interfacesOften includes additional security features and integrations- Comprehensive container management - Suitable for development environments
Specialized runtimesRuntimes tailored for specific platforms or use cases, like Kubernetes or edge computing- Optimized for specific platforms - May include features for specific environments like IoTVaries based on the specific runtime and its intended use caseVaries, but often includes optimizations for specific environments or platformsMay include specialized security features for the targeted platform or use case- Kubernetes deployments - Edge computing and IoT-focused applications

Popular container runtime tools

Several tools have gained prominence in containerization due to their capabilities and widespread use. The following table summarizes the most popular tools and their features:

Runtime toolDescriptionKey featuresSecurityUse cases
DockerAn all-encompassing platform for creating, deploying, and operating applications in containers- User-friendly interface - Integrated container orchestration - Image management - Cross-platform support- Integrated security features - Regular updates and patches- Comprehensive container management - Suitable for both development and production environments
containerdA standard container runtime in the industry, emphasizing ease of use, reliability, and cross-platform compatibility- OCI Image Format support - Image push and pull support - Multi-tenant support-OCI Runtime Spec support- Secure by design, with a focus on standard compliance - Regular vulnerability scanning- Comprehensive container management - Suitable for both development and production environments
runCA command-line interface tool for initiating and managing containers based on OCI standards- Low-level operation - Direct interaction with OS - Lightweight and minimalistic - Focus on container execution- Basic, reliant on host OS security features - Supports secure configurations- Scenarios requiring direct interaction with container processes - High degree of control and customization
CRI-OA streamlined container runtime tailored for Kubernetes environments- Optimized for Kubernetes - Supports OCI container images - Uses CNI for networking - Secure by default- Designed with Kubernetes security in mind - Regular updates to address Kubernetes specific threats- Kubernetes deployments - Environments prioritizing efficiency and Kubernetes compatibility
PodmanA community-driven tool for handling containers and pods, fully compatible with Kubernetes systems- Daemonless and lightweight - Compatible with Docker - Kubernetes-ready - Cross-platform support- Rootless operation enhances security - Supports secure configurations and policies- Secure, lightweight container management - Environments where security is a priority - Kubernetes-compatible deployments

In this comparison, Docker stands out as a versatile and user-friendly platform, ideal for developers who need an integrated environment for building, shipping, and running applications. containerd and runC, on the other hand, offer more specialized and lower-level functionalities, focusing on the core aspects of container runtimes with a lean approach. CRI-O is optimized for Kubernetes, making it a go-to choice for those deeply invested in Kubernetes ecosystems. Lastly, Podman distinguishes itself by enabling daemonless container management, offering a unique approach that aligns well with security-focused and minimalistic environments. 

This range of options reflects evolving and diverse needs in the world of containerization, providing tailored solutions for various deployment strategies and operational requirements. 

Security implications

Container security is essential because these features safeguard containerized environments, which are inherently more complex than traditional workloads. The challenges include:

  • Larger attack surface: The attack surface is significantly larger than traditional workloads due to the multitude of containers and their various underlying images.

  • Shared kernel architecture: Containers share the underlying kernel of the host system. Securing the host alone is insufficient; maintaining secure configurations for container isolation is critical. Because any vulnerabilities in the container setup can potentially compromise the entire host system, it’s vital to maintain secure and isolated configurations for each container to ensure overall system integrity and security.

  • Dynamic environments: The highly dynamic nature of containerized workloads poses visibility challenges, making it difficult for traditional monitoring tools to keep track.

Best practices for secure container deployment

Adopting a holistic security strategy is the only way to protect container deployments. An ideal strategy should encompass everything from image creation to runtime monitoring, including:

  • Securing images: Ensure container images are free from vulnerabilities by scanning and removing vulnerabilities from them before deployment. 

  • Securing registries: Implement access control and image signing in container registries.

Securing deployment: Reinforce the base host operating system, implement robust firewall regulations, and utilize container orchestrators that provide secure API endpoints and enforce role-based access control (RBAC). Additionally, configure containers to run with the least privilege necessary. Avoid running containers with root or high privileges, and ensure that images do not contain embedded secrets.

Monitoring container activity: Implement granular monitoring to provide visibility into container health and behavior. 

Understanding the sophistication of container isolation, network security, and the specific vulnerabilities associated with container environments is critical for a comprehensive security posture. For an in-depth exploration of container runtime security, including advanced topics and the latest trends, check our detailed blog post about container runtime security.

Conclusion

The future of container runtimes will be characterized by continued innovation and growth. As cloud-native architectures become increasingly prevalent, container runtimes will evolve to offer even more robust, efficient, and secure solutions. Whether you are a developer, operations professional, or security expert, it’s imperative to stay informed and adapt to the latest container runtime trends and technologies. Prioritize learning, explore emerging tools, and consistently place a high emphasis on security within your container-based setups.

For those interested in enhancing their container and Kubernetes security, Wiz offers a comprehensive container and Kubernetes security solution. Our suite of tools provide a holistic approach to securing containers and Kubernetes, ensuring your applications are protected from build-time to real-time. To learn more about how Wiz can help secure your container environments and streamline your security processes, schedule a demo with Wiz today!

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