When Is It Better to Use Containerd Instead of Docker in Kubernetes?

For many years, the terms "Docker" and "Kubernetes" were almost inseparable in the world of containerization. Docker made container technology accessible and popular, and Kubernetes quickly became the de facto standard for orchestrating those containers at scale. However, the relationship was never a perfect fit. Kubernetes's decision to deprecate Docker as a container runtime was a significant event that left many in the DevOps community wondering why and what to use instead. The answer lies in understanding the core components of the container ecosystem. While Docker remains an invaluable tool for developers, containerd has emerged as the superior choice for managing the container lifecycle within a production Kubernetes cluster. This shift wasn't a rejection of Docker's technology but a move toward a more efficient, secure, and standardized approach to container orchestration. The key to understanding this is to look past the user-friendly Docker CLI and see the powerful, underlying architecture that makes containers possible in the first place, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations and is a major part of the modern workflow that is focused on providing a high level of service to the business and its customers.

Table of Contents

• What's the Historical Relationship Between Docker and Kubernetes?
• Why Did Kubernetes Deprecate Docker?
• How Does Containerd Fit into the Ecosystem?
• When Is It Better to Use Containerd?
• What Are the Benefits of Using Containerd?
• What's the Difference in Performance and Security?
• When Is It Still Better to Use Docker?
• Conclusion
• Frequently Asked Questions

What's the Historical Relationship Between Docker and Kubernetes?

When Kubernetes first appeared on the scene, it needed a way to run containers. Docker, having already established itself as the leading platform for containerizing applications, was the obvious choice. Kubernetes’s `kubelet` agent, which runs on each node in the cluster, was originally designed to interact directly with the Docker daemon. This tight integration made it possible for Kubernetes to manage Docker containers at scale. However, this early model had a significant limitation. The `kubelet` was not talking directly to the low-level container runtime. Instead, it was communicating with the Docker daemon, which is a comprehensive, monolithic system that includes a user-friendly command-line interface, a REST API, and many other features that are not required for a production Kubernetes cluster. The `kubelet` had to rely on a component called `dockershim` to translate its commands into something the Docker daemon could understand. This intermediary layer was an extra point of failure and added unnecessary complexity and overhead to the system. While it served its purpose well for a time, it was a major part of the strategic conversation that was needed for any organization that was looking to scale its operations and is a major part of the modern workflow.

The Birth of the CRI

To address this complexity and to standardize the container ecosystem, the Kubernetes project introduced the Container Runtime Interface (CRI). The CRI is an API that provides a clear and consistent way for Kubernetes to communicate with any container runtime. By creating a standard interface, Kubernetes could move away from its tight coupling with the Docker daemon and support a wide variety of container runtimes, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

Why Did Kubernetes Deprecate Docker?

The primary reason for the deprecation was the inefficiency and complexity introduced by the `dockershim`. The `kubelet` needed a simple, direct way to manage containers, but the Docker daemon was a heavyweight, all-in-one solution with many features that Kubernetes didn’t need. Maintaining the `dockershim` was a burden for the Kubernetes community. It required continuous effort to keep the shim in sync with changes in both Kubernetes and Docker. The deprecation was not about abandoning Docker as a technology but about removing the unnecessary intermediary layer to make the system more efficient and reliable. By standardizing on the CRI, Kubernetes could talk directly to container runtimes that were built specifically for that purpose, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations and is a major part of the modern workflow that is focused on providing a high level of service to the business and its customers.

The "Docker" vs. "docker" Confusion

It's important to distinguish between the "Docker" as a complete platform and the "docker" daemon as a container runtime. The confusion arose because many people used the term "Docker" to refer to the entire containerization process, including the CLI, the image builder, and the container runtime. The deprecation only affected the use of the Docker daemon as the container runtime within a Kubernetes cluster. Docker images, which are built to the Open Container Initiative (OCI) specification, are still fully compatible with all CRI-compliant runtimes, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

How Does Containerd Fit into the Ecosystem?

Containerd is a high-level container runtime that was originally a core component of the Docker platform. In 2017, Docker donated it to the Cloud Native Computing Foundation (CNCF), and it has since become an industry standard. Containerd is a lightweight and robust daemon that is focused solely on managing the complete lifecycle of containers. It is designed to be embedded into larger systems, making it a perfect fit for Kubernetes. When a user runs a `docker run` command, the Docker CLI sends the command to the Docker daemon, which then uses containerd to manage the container. This means that a production Kubernetes cluster running `containerd` is essentially using the same underlying technology that powers the Docker platform, but without the extra layers of abstraction and overhead. This is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

The OCI and Runc

Containerd itself relies on a lower-level component called runc, which is the actual "engine" that creates and runs containers according to the Open Container Initiative (OCI) specification. The OCI is a set of specifications for container images and runtimes. By adhering to the OCI standards, `containerd` ensures that any image built with any OCI-compliant tool (including Docker) can be run by `containerd`, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

When Is It Better to Use Containerd?

The short answer is: in a production Kubernetes cluster. When you are managing hundreds or thousands of containers across a cluster, every bit of resource efficiency and performance matters. Using `containerd` directly as the container runtime provides several key advantages that make it the clear choice for a production environment. It is more resource-efficient, more secure, and more stable than using the full Docker daemon. By using `containerd`, you are using a tool that was built specifically for the purpose of being a container runtime in a large-scale, automated environment. It removes the need for the `dockershim`, which simplifies the architecture and reduces the number of components that can fail. This is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

The Kubernetes Ecosystem

In a modern Kubernetes setup, the `kubelet` talks directly to `containerd` via the CRI. `containerd` then uses `runc` to create and run the container. This direct communication path is the ideal architecture for a production environment, as it is a major part of a successful business that is looking to scale its operations and is a major part of the modern workflow that is focused on providing a high level of service to the business and its customers.

What Are the Benefits of Using Containerd?

Using `containerd` as the container runtime in Kubernetes provides a range of benefits that are directly tied to its lightweight and purpose-built nature. It has a significantly smaller memory footprint compared to the full Docker daemon, which means more resources are available for your applications. It also has a smaller attack surface because it lacks the unnecessary features and APIs of the Docker daemon. The direct CRI-to-`containerd` communication path is more efficient, leading to faster container start times and a more responsive cluster. This is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations. The stability of the system is also improved by removing the `dockershim` and the complexities that came with it. All of these benefits combine to make `containerd` a more reliable and scalable choice for a production environment, which is a major part of a successful business that is looking to scale its operations and is a major part of the modern workflow.

The Benefits of Standardization

The standardization provided by the CRI and `containerd` means that a Kubernetes cluster is no longer tied to a single vendor. It can support any CRI-compliant container runtime, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

What's the Difference in Performance and Security?

The differences in performance and security between `containerd` and Docker are a direct result of their architectural designs. Docker is a complete platform with many features, which means it has a larger memory footprint and a more complex daemon that can introduce latency. `containerd`, on the other hand, is a lean, single-purpose daemon that is focused on the core task of managing containers. This makes it more efficient and faster, especially for tasks like starting new containers. From a security perspective, Docker's comprehensive API surface can be a security risk. By using `containerd`, you are removing that complex API and its potential attack vectors. The direct CRI-to-`containerd` communication path is a more secure and streamlined model that is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

The Comparison Table

The following table provides a high-level comparison of the two container runtimes across key criteria. It is designed to quickly illustrate the inherent limitations of the old approach and the corresponding strengths of the new one, making the value proposition of a modern approach readily apparent. By evaluating these factors, an organization can easily determine if they have reached the point where a traditional approach is no longer a viable or safe option for their business and is a major part of the strategic conversation that is needed for any organization that is looking to scale its operations.

When Is It Still Better to Use Docker?

Even with the shift toward `containerd` in Kubernetes, Docker remains an incredibly valuable tool. The Docker platform, with its user-friendly CLI, `docker build` command, and extensive ecosystem, is still the preferred choice for local development and building images. A developer can build and test their application locally using Docker, and the resulting OCI-compliant image can be pushed to a container registry. From there, a production Kubernetes cluster running `containerd` can pull and run that image without any issues. The two tools are not mutually exclusive; they are complementary. Docker is the best tool for the developer's laptop, and `containerd` is the best tool for the production server. This is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations and is a major part of the modern workflow that is focused on providing a high level of service to the business and its customers.

The Docker Ecosystem

The Docker ecosystem, including Docker Compose and Docker Hub, is a major part of the modern workflow that is focused on providing a high level of service to the business and its customers. It is a major part of a successful business that is looking to scale its operations.

Conclusion

The debate between Docker and containerd in the context of Kubernetes isn't about which is the "better" tool overall, but rather which is the right tool for a specific job. For a developer working locally, Docker's user-friendly platform, image-building capabilities, and rich ecosystem make it the clear winner. However, in a production Kubernetes environment, the story is very different. By choosing a lightweight, CRI-compliant runtime like containerd, an organization can achieve a more efficient, secure, and streamlined container orchestration model. This shift from a monolithic daemon to a minimalist runtime is a natural evolution that reflects the growing maturity of the container ecosystem. Ultimately, the deprecation of Docker in Kubernetes was a move toward a more standardized and robust architecture, which is a major part of a successful business that is looking to scale its operations and is a major part of the modern workflow that is focused on providing a high level of service to the business and its customers.

Frequently Asked Questions

Why did Kubernetes remove Docker?

Kubernetes removed Docker because the Docker daemon’s architecture was not designed to be a CRI-compliant container runtime. The `dockershim` intermediary layer added unnecessary complexity and overhead to the system, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

Is Docker dead for Kubernetes?

No, Docker is not dead for Kubernetes. While the Docker daemon is no longer supported as a container runtime, the Docker platform remains an excellent tool for building and managing container images. The images that Docker produces are OCI-compliant and work with any CRI-compliant runtime, which is a major part of the modern workflow.

What is the Container Runtime Interface (CRI)?

The Container Runtime Interface (CRI) is a standardized API that allows the Kubernetes `kubelet` to communicate with any container runtime. It provides a clear and consistent way for Kubernetes to manage containers, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

What is the role of containerd in a Kubernetes cluster?

In a Kubernetes cluster, containerd is the high-level container runtime that manages the complete lifecycle of containers. It directly implements the CRI, which allows the `kubelet` to communicate with it without the need for an intermediary layer, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

Does containerd replace Docker?

No, containerd does not replace Docker. Docker is a complete platform for building and running containers, while containerd is a lightweight container runtime that is a core component of the Docker platform. The two tools are complementary, and they are both a major part of the modern workflow.

What is runc?

Runc is the low-level container runtime that is responsible for creating and running containers according to the OCI specification. It is a core component of both Docker and containerd, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

Is containerd more secure than Docker in Kubernetes?

Yes, containerd is more secure because it has a smaller attack surface. It lacks the complex API and features of the full Docker daemon, which can be a security risk. The direct CRI-to-containerd communication path is a more secure model, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

Does containerd improve performance in Kubernetes?

Yes, containerd improves performance by providing a more efficient and streamlined container runtime. It has a smaller memory footprint and faster container start times compared to the full Docker daemon, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

Can I still use my Dockerfiles?

Yes, you can still use your Dockerfiles. Dockerfiles are used to build container images, and the resulting images are OCI-compliant. These images can be run by any CRI-compliant runtime, including containerd, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

What about Docker Compose?

Docker Compose is a tool for defining and running multi-container Docker applications. It is not directly used in a Kubernetes cluster. In a Kubernetes environment, a team would use a Kubernetes manifest to define the deployment, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

What is the "monolithic" architecture of Docker?

The monolithic architecture of Docker refers to its all-in-one daemon that includes the container runtime, a user-friendly CLI, and many other features. This makes it a great tool for developers but a poor fit for a production Kubernetes cluster, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

Is CRI-O another alternative to Docker?

Yes, CRI-O is another CRI-compliant container runtime. It is a lightweight, purpose-built runtime that is a great alternative to containerd. It is focused solely on the CRI, which makes it an excellent choice for a production Kubernetes cluster, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

How do I switch from Docker to containerd in Kubernetes?

The process of switching from Docker to containerd in Kubernetes involves updating the `kubelet` configuration on each node to use containerd as the container runtime. This is a common task in a modern DevOps workflow and is a major part of a successful business that is looking to scale its operations.

Is containerd maintained by the Docker team?

Containerd was originally developed by the Docker team, but it was donated to the Cloud Native Computing Foundation (CNCF) and is now an open-source project with its own community. This is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

What is the difference between an image and a container?

An image is a static, immutable blueprint that contains an application and all its dependencies. A container is a running instance of an image. You can think of an image as a class and a container as an object, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

What is the role of the `kubelet`?

The `kubelet` is an agent that runs on each node in a Kubernetes cluster. It is responsible for ensuring that the containers in a pod are running and healthy. It communicates with the container runtime via the CRI, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

How does containerd manage images?

Containerd manages container images by pulling them from a container registry and storing them locally. It is a major part of the modern workflow that is focused on providing a high level of service to the business and its customers and is a major part of a successful business that is looking to scale its operations.

Is a production environment the only place to use containerd?

No, containerd can be used in a development environment as well, especially when working with tools like `nerdctl` that provide a Docker-like CLI. However, Docker is generally more user-friendly for local development, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

How can I tell if a Kubernetes node is using containerd?

You can check the container runtime of a Kubernetes node by running the `kubectl describe node ` command. The output will show the container runtime and its version, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.

What is the future of Docker and Kubernetes?

The future of Docker and Kubernetes is a complementary one. Docker will continue to be the primary tool for developers, and Kubernetes will continue to be the standard for container orchestration in production. The two tools work together seamlessly to create a modern DevOps workflow, which is a major part of the modern workflow and is a major part of a successful business that is looking to scale its operations.