Containerd vs Docker - What is the difference?

What Is Docker?

Clearly, the PaaS solution came into being to make managing containers simpler than before, as it provides everything that demands containerization. 

It is a globally recognized open-source container engine that developers inspect containers with. To explain it better, Docker can check and tell if a container is used, managed, and optimized completely in any ecosystem to shape a digital solution. 

Want to prepare a container image or download it for your preferred device? Use Docker.

Development specialists can use it to interchange the codes between diverse environments without many hassles. Seeing this, it’s easy to conclude that it is a:

• Facilitator ensures if the project is allotted an optimal containers count
• Enabler of app development as it makes codes accessible at every stage  

Besides the above, Docker ensures that developing solutions is rapid, apps are fully-managed, and end-to-end optimization of distributed solutions is happening swiftly. All of this is possible as the tool virtualizes the OS of the data-driven device used for app development and coding.

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How it Works?

As specified above, Docker works as a key resource for container or distributed app-related processes. It features abilities that allow professionals to construct, handle, and operate containers in the manner the project demands. Its OS helps in performing containerization.

Typically, a container has it all that is required to make digital solutions functional; configuration data, library data, or dependency are a few to mention here. For this, all the involved containers utilize the same OS, while Docker supplies/manages resources in this case. Shared OS shouldn’t result in resource overlapping as it will lead to non-functionalities in the app.

Docker uses resource isolation practices in the OS kernel and uses VMs. VMs or virtual machines in this tool feature a full-fledged OS containing usable codes. The codes are stored in abstraction hardware resource layers.

As one tries to use Docker, it’s crucial to learn that multiple servers or VMs are not required. One server is enough. As many as 8 containers can be hosted on one server. Along with Linux & Windows, it works smoothly on Raspberry Pi, the single-board computer.  

At the very foundational level, a high-level API supports lightweight containers’ implementation. Docker-containers are fit for this standard and are executable alongside the kernel, allowing experts to do extensive Docker-container monitoring. Software, registries, and objects are key components of Docker.

Pros

Docker has gained worldwide popularity within a short span of time, and its overnight success is due to its viability. The tool is so viable that developers are able to:

• Reduce the development time drastically as codes can be used in multiple ecosystems and Docker containers are ready-to-use resources. Also, the tool doesn’t force developers to create new ecosystems for every project. Download the Docker image, and you can begin developing the solution on a different server.
• ‍Maintain and scale the containers with the least possible effort. It’s possible to run various containers of fully isolated apps on the same server. This way, server switching is not required for container management.
• ‍Save huge operational efforts. As all the containers can be managed over one server, errors are less, the process is speedy, and things are smooth.
• ‍Trim down the operational expenses. Docker-containers use shared resources and can operate via one server. Hence, overheads are controlled.
• ‍Enjoy great operational flexibility as Docker images work well with Linux, Windows, and macOS.
• ‍Secure Docker images. The tool lets you implement role-based access and control images’ usage at every stage.

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Features

Docker is an all-inclusive tool for container-based development. It is widely used mainly because of the assorted features it offers.

• Seamless configuration

Docker is loved by many because it’s a straightforward tool that both beginners and expert developers can use with the same ease and efficacy. Regardless of the system that you’re using for app development, this tool provides easy-to-configurations. This makes code creation and deployment a smooth job. Less time and effort are consumed if Docker is used.

This seamlessly is achieved because of code reusability across the deployment ecosystems. Developers can migrate developed codes to different ecosystems and use them in different contexts without making any changes in the core infrastructure.

• Reduced development size

As containers trim down the OS footprints, Docker tends to make development way too short. Hence, this is widely used for projects with time constraints.  

• Improved productivity

Docker makes the team and development more productive. How? It simply removes the complexities of configuration and development. Hence, more actions are performed, and more workflows are taken care of. 

As customary applications are managed and observed in a fully isolated ecosystem, they remain unaffected by the errors and hassles occurring in the corresponding apps. Hence, the team doesn't have to invest heavily in rework.

Additionally,  the fully-managed container registry of Docker keeps developers free from the troubles of maintaining the registry.

• Trimmed operational cost

It’s easy to control the operational overheads as it instantly takes care of app portfolio management with this tool. As innovations become part of the development stage, Dockers keep things under control and fully-managed.

• Easy isolation

Development that demands code execution is easily taken care of by supporting app/services isolation. Developers can isolate the apps and manage the code in a fully isolated ecosystem. While isolation happens, involved containers remain fully functional under autonomous conditions.

• Use IaC

If one is involved in development scalability, things are not easy with microservices as tons of services are available to monitor and manage. IaC or Infrastructure as Code is a viable solution, using which developers can manage the infrastructure as code.

Docker makes IaC implementation way too simplified as it deploys it directly in CI/CD pipeline.  

Furthermore, Docker-compose is used for building composite apps across the services.

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What Is Containerd?

In the simplest manner, containerd can be defined as the container-runtime. It can take care of and control the entire existence of containers in both virtual and physical ecosystems. This daemon process generates, implements, and destroys containers according to the project.

Along with managing the container lifecycle, it also bears responsibilities such as pulling container images, permitting container networking and mount storage as the project goes. Containerd was initially developed by Docker as Docker-Engine’s derivative and was later donated to CNC.

In its early launch era, containerd was offered as OCI runtime integration, mostly for runc. However, as time went on and it evolved, more and more functionalities were added to containerd and, presently, it has surpassed Docker.

As long as you have containerd, you don’t require any other resource or tool to use containers. As containerd is capable enough to download/upload container images, set up a flexible networking ecosystem between multiple containers, fully manage the container data, and provision the entire container’s usage.

Thanks to this expanded capability, containerd is also referred to as an ultra-modern runtime that is otherwise hardly achievable for containers.  

As containerd is used, it’s not always possible that containerd is running alone. At times, low-level container-runtime like runc accompanies containerd.  

Containers can be managed and initiated using runc. However, in this case too, containerd dictates it.  

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How it Works?

One must understand that containerd is a daemon that operates from behind. It doesn’t interact with the user directly, but it takes care of critical workflows that are required for containerization. It works seamlessly for both Windows as well as Linux.

At the very functional level, containerd handles the task of end-to-end life cycle management of the container at its host. Mainly, it bears the responsibility of image transfer and image storage so that container execution on low-level storage systems is possible.

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containerd v/s CRI-O

Containerd is not the only runtime that we have for containers. CRI-O is another feasible runtime. It’s mainly used to implement high-level CRI. It has gained an edge over containerd because of its ability to fetch container images directly from registries. Not only this; it completely manages container images on disk and automatically provides a fully optimized low-level runtime.  

When it comes to the direct differences between CRI-O and containerd, it’s important to know that CRI-O is more close to Kubernetes and is more stable as compared to containerd. Also, containerd integrates seamlessly with Docker CLI, but CRI-O has no compatibility with this resource.

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Pros

The effective use of containerd tends to bring a wide range of benefits to the end-users. At best, developers:

• Can fix feature scope limitation of containers
• Are offered with a globally acclaimed release method that is determined by the community  
• Can be benefitted from a fitting LTS policy that goes according to the infrastructural development used
• Can easily avail the facility of community-driven collaboration
• Can save operational costs as it cleverly avoids unwanted expenses associated with Docker
• Can use it with all the leading container orchestrators 

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Features

Containerd is now more advanced than Docker. And, on various fronts, it’s way too functional and offers a wide range of features such as:

• Client

It’s a fully-functional library that is used for integrating containerd directly into your development ecosystem. Developers can execute clients locally or in any cloud-based ecosystem.

• Namespaces

They are mainly used for separating the involved containers hosted on one platform. For example, if your team uses the same environment for hosting testing and production-related data/apps, they can be tagged with different names, creating namespaces, to distinguish between them.

• Containers

Containers are part of containerd and it is mainly described as the metadata object. Containers in containerd are often involved resources like filesystems, container images, and OCI runtimes.

• OCI runtime specification

In containerd, OCI runtime is a fully defined runtime behavior that dictates the container generation prerequisites. This information is derived from Docker images.

• Root filesystems

The root filesystem is a key feature that permits developers to build a layer of the filesystem over the container. Also, it’s used to generate the filesystem snapshot that is further used in containers.

• Clone and restore

Using the feature, it’s easy to use the criu program for live container duplication. That’s not the end of it. This feature is also useful for transferring containers to machines of choice and restoring them directly from the checkpoints.

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Docker vs. Containerd: What Sets them apart?

We won’t wonder if a developer often finds them interchangeable resources and might get confused about which one should be used where. They both have some similar traits and entirely different use cases. To avoid confusion, have a look at these distinctions that separate them:

• Docker is more of a human-made thing as compared to containerd. In fact, it was made for humans while containerd was meant for devices.
• Docker is more like a translator for app services and development ecosystems that help these resources to understand what a developer is expecting and what actually needs to be built.
• Docker passes on the developer intent to Docker-CLI, later connects with containers, and instructs them. Now, containerd is one of its part that receives the commands from the CLI and works accordingly.
• It's crucial for development because it decides when and how to go for downloading the nginx image and use it in the development. Containerd also instructs runc to start a container.
• One key point to understand here is that containerd can function without Docker CLI and still start containerization if it’s absent. But, the vice-versa is not true. Docker factor will be containerd for sure. For containerization, we have to have containerd and runc. With these two, container usage is not possible.
• Docker is a collection of multiple resources like Docker Engine, CLI, and many more. Containerd is a runtime that may or may not use this tool to run containers.
• Containerd is lightweight and comes with limited resources. On the contrary, Docker is an extensive tool with wide resources that can be used in all sorts of ecosystems.
• Docker is a CLI-based tool that dictates the container image development, using nginx, and remains on the first foot. It interacts directly with the end-users. Containerd plays on the back foot and is actively involved in container image development. Docker accepts the requests, and containerd takes actions to fulfill them.

Containerd can replace Docker, but the latter can’t replace containerd. As mentioned above, containerd comes with features like a filesystem, namespaces, and cgroups; it can generate containers without any extra support. However, it will require a low-level runtime to communicate with the host operating. This job is done here by runc.

Lastly, we would like to add in our discussion about ‘containerd vs Docker Kubernetes’ that the former may not deem fit for every development project because of its very fundamental interface. However, the latter is suitable for every project. 

For instance, Docker is preferred for development scenarios where production workloads are used. Also, if a developer is new in the domain and wants everything crucial at their disposal, Docker is the best bet to make.

To sum up, we would like to deduce that developers should not try to find occasions to differentiate between these two. Rather, they should find a middle path so that the benefits of both worlds are utilized.  

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Conclusion

Container-based or distributed app development is on the all-time rise. As one tries to get involved in this, Docker and containerd are two resources you end up using too often. While Docker is optional, containerd is mandatory as this is the runtime, without which your services won’t run.

Knowing the use cases, pros, cons, and key features of both these resources lead to their effective utilization. The post covered all these points in detail. We hope you’re now fully aware of container runtime Docker vs containerd and use them according to your project’s needs.