Containerized, Docker, and Cri-o are among the top contenders of container runtimes. This blog will break down these container runtimes in simple terms to help you make an informed decision.
In this article, we compare the most popular container runtimes - Docker vs Containerd vs Cri-o. Let's start by looking at what these runtimes are and how they work.
- What is Containerd?
- How Does Containerd Work?
- Revisiting Docker
- How Does Docker Work?
- What is Cri-o?
- How Does Cri-o Work?
- Docker vs Containerd vs Cri-o - Head-to-head Comparison
- Docker vs. Containerd vs. Cri-o - Performance
- Docker vs. Containerd vs. Cri-o - Implementation
- Docker vs. Containerd vs. Cri-o - Limits
- Docker vs. Containerd vs. Cri-o - Networking
- Docker vs. Containerd vs. Cri-o - Pros & Cons
What is Containerd?
Containerd is an open-source runtime that offers a vital infrastructure layer for managing containers on the host system. Simply put, it's more like an "engine" that handles the creation, execution, and deletion of the containers.
This makes it easier to manage and run applications in isolated environments.
Now talking about the history, Containerd was initially developed by Docker, Inc., as a part of the Docker Project. And it got amazing popularity in the early days of containerization.
As the adoption of containers started increasing, it became evident that the container's functionality could benefit the broader container community beyond just Docker's ecosystem.
And to facilitate this, Docker donated Containerd to the Cloud Native Computing Foundation (CNCF) in March 2017.
By doing so, Containerd became a standalone project and gained a more vendor-neutral and community-driven development approach.
Also Read: Consul vs Istio vs Containerd
How Does Containerd Work?
When users tell Docker or Kubernetes to run a container, they communicate with Containerd to complete the job. Containerd manages all the details of the Container lifecycle management.
This is to ensure the availability of images whenever the customer wants to run a container based on that image.
When the user asks Containerd to create a new container, it uses the image that they have specified and sets up an isolated environment for their applications.
This environment includes everything the app needs to run independently, like its file system, networking, and process space.
Once the container is up and running, Containerd oversees all the processes. It helps users to start, stop, or delete these containers with a single command.
Containerd is also designed to be extensible, allowing developers to add extra features and functionality.
Also Read: How to Cleanup Docker Resources?
Docker is among the widely used platforms that simplify the process of building, deploying, and running applications inside containers. It offers an easy-to-use interface that lessens the complexity of containers.
Docker makes it easy for developers to use containers effectively.
Docker was first introduced in March 2013 by Solomon Hykes and his team at dotCloud, a platform-as-a-service company.
The release of Docker was a hit in the developer community because it revolutionized how applications were packaged and distributed.
Also Read: Differences between Docker and Podman
How Does Docker Work?
Docker simplifies the process of managing applications by packaging them inside containers. To do this, first, you need to write a DockerFile.
In this, you need to specify what their app needs, like the base operating system, the programming language, and any dependencies it relies on.
Once you get your Dockerfile set up, you can run a simple command (docker build) to build their container image.
This process takes all the information from the Dockerfile and creates a lightweight, standalone package.
And once the container image is ready, users can easily share it with others or move it to different environments without worrying about compatibility issues.
When it's time to run the app, users fire up a container based on their created image.
Docker sets up a secure and isolated environment for the app to run in, ensuring it's shielded from the rest of the system and other containers.
Also Read: Kubernetes vs Docker Swarm
What is Cri-o?
Cri-o, or Container Runtime Interface - Orchestrator, is an open-source container runtime designed specifically for Kubernetes. It provides seamless integration between Kubernetes and container runtimes. This allows Kubernetes to manage containers efficiently and effectively.
Talking about history, It was introduced by the Open Container Initiative (OCI) in October 2016. The OCI is a community-driven project that develops open standards for container formats and runtimes.
Following OCI standards, Cri-o ensures compatibility with other container tools and runtimes, promoting a more diverse and interoperable container ecosystem.
Also Read: Kubernetes Pods vs Nodes vs Clusters
How Does Cri-o Work?
Cri-o is a container runtime specifically designed to work with Kubernetes. Its primary function is to manage containers efficiently and securely within a Kubernetes cluster.
When users want to deploy a containerized application to their Kubernetes cluster, they create Kubernetes Pod specification. They define the desired state of the user's application.
This Pod specification is passed to the Kubernetes control plane, which interacts with Cri-o using the Container Runtime Interface (CRI) API.
Cri-o then takes over and performs several essential tasks. First, it pulls the container image specified in the Pod specification from the container registry, such as Docker Hub or any other OCI-compliant registry.
Once the container image is available locally, Cri-o sets up an isolated environment for the container to run.
This isolation ensures that the container operates independently and does not interfere with other containers or the underlying host system. Security and stability are key aspects that Cri-o emphasizes during this process.
Containerd vs Docker vs Cri-o - Head-to-head Comparison
Docker is an all-in-one container platform known for its user-friendliness. It offers a complete set of tools to build, deploy, and manage containers easily.
It has rich features such as Docker Compose and Docker Swarm. That makes it suitable for various use cases, and its wide adoption has made it a staple in the container ecosystem.
Containerd is a lightweight and modular container runtime focused on execution and management. It's designed for resource and performance optimization.
This makes it ideal for environments with limited resources or scenarios where performance is critical. While it may lack some high-level features, its extensibility allows developers to tailor it to their needs.
Cri-o is purpose-built for Kubernetes and offers seamless integration with Kubernetes clusters.
It adheres to the Kubernetes-native approach, providing a secure and efficient container runtime.
Cri-o prioritizes compatibility with Kubernetes, following the Kubernetes CRI API and focusing on container isolation to enhance security.
Also Read: Kubeadm Tutorial
Docker vs. Containerd vs. Cri-o - Performance
Docker offers a wide range of features and functionalities. But that also means it might have a slightly larger memory and resource footprint than the other two.
While Docker's versatility is excellent for various use cases, its all-in-one nature can lead to more overhead when running containers.
Containerd, on the other hand, is all about efficiency and speed. It focuses specifically on container execution and management. This makes it lightweight and optimized for performance.
If you're looking for a container runtime that conserves resources and performs well in resource-constrained environments, Containerd is a good choice.
Cri-o also prioritizes performance, especially in Kubernetes environments. Being purpose-built for Kubernetes, Cri-o integrates seamlessly with Kubernetes clusters and maintains a low resource overhead.
Its streamlined design and focus on Kubernetes-native integration contribute to faster container startup times and smoother performance within a Kubernetes setup.
Containerd vs Docker vs. Cri-o - Implementation
Docker is like a versatile all-in-one package. It offers a full-fledged platform with a user-friendly command-line interface (CLI) and a graphical interface.
Docker has everything you need to build, deploy, and manage containers effortlessly. Docker uses its runtime to execute containers, managing all aspects of the container lifecycle.
It also offers other functionalities like image management, networking, and storage. That makes it a comprehensive solution for containerization.
Containerd, on the other hand, takes a more focused approach. It serves as a core container runtime designed to be lightweight and modular.
Containerd handles container execution and management, leaving out some higher-level features in Docker.
However, its modular architecture extends it with additional functionalities as needed.
Cri-o is like the dedicated sidekick to Kubernetes. It is purpose-built to be the container runtime for Kubernetes clusters.
Cri-o follows the Kubernetes Container Runtime Interface (CRI) standard, making it a seamless fit for Kubernetes.
It bridges Kubernetes and the underlying container runtime, ensuring that Kubernetes can efficiently manage containers with Cri-o's support.
Also Read: Docker Commands Cheat Sheet
Docker vs. Containerd vs. Cri-o - Limits
Even though Docker is feature-rich and versatile, the broad range of functionalities also comes with a trade-off. Docker can have a larger memory and resource footprint than specialized container runtimes like Containerd and Cri-o.
So, Docker might not be the most optimal choice in resource-constrained environments.
Containerd takes a more minimalist approach. It focuses solely on container execution and management, keeping things lightweight and efficient.
While it's excellent for running containers with a smaller resource overhead, Containerd might lack some of the higher-level features found in Docker.
Cri-o is like a dedicated expert for Kubernetes. It integrates seamlessly with Kubernetes clusters and follows Kubernetes' native approach through the CRI API.
This specialization makes Cri-o a fantastic fit for Kubernetes environments. However, since it's designed specifically for Kubernetes, it might not be as feature-rich or suitable for non-Kubernetes use cases.
Containerd vs Docker vs Cri-o - Networking
Docker has built-in networking features that make it easy to manage container networking.
It offers various networking options, such as bridge, overlay, and host networking. This allows containers to communicate with each other and the outside world.
Docker's default bridge network enables containers on the same host to communicate by default.
However, users can also create custom networks to isolate containers or enable communication across multiple hosts.
Containerd, a core container runtime, focuses primarily on container execution and management and does not include built-in networking capabilities like Docker.
However, Containerd can be used alongside container networking solutions like CNI (Container Networking Interface) plugins.
Cri-o follows the Kubernetes-native approach, which leverages Kubernetes' built-in networking capabilities.
Kubernetes provides its networking model, allowing containers in different pods to communicate through the Kubernetes Service abstraction.
It uses CNI plugins for container networking, just like Containerd.
Also Read: Top Kubernetes Distributions
Docker vs. Containerd vs. Cri-o - Pros & Cons
Pros of Docker
Comprehensive Platform: It offers an all-in-one solution with a user-friendly interface, making it easy to build, deploy, and manage containers.
Rich features: It provides various features like Docker Compose for multi-container orchestration and Docker Swarm for clustering.
Massive Community: Docker has widespread adoption and a massive community, providing extensive resources and support.
Cons of Docker
Resource Overhead: Since Docker has feature rich nature, It can lead to a larger memory and resource footprint compared to more lightweight runtimes.
Complexity: The abundance of features might be overwhelming for some use cases, and not all features may be necessary for certain environments.
Pros of Containerd
Lightweight and modular: Containerd is designed for performance and efficiency, making it suitable for resource-constrained environments.
Extensibility: Its modular architecture allows developers to customize and extend it with additional functionalities.
Great Industry Adoption: Containerd has gained popularity and strong industry support, becoming a core component in various container platforms.
Cons of Containerd
Minimal Features: Containerd focuses solely on container execution and management, lacking some higher-level features in Docker.
CLI Complexity: The CLI is more low-level than Docker, requiring more manual configuration for certain tasks.
Pros of Cri-o
Kubernetes-native: Cri-o is purpose-built for Kubernetes, offering seamless integration and adherence to Kubernetes CRI standards.
Performance and Security: It prioritizes performance with low resource overhead and emphasizes container isolation for enhanced security.
Simplicity: Cri-o's streamlined design makes it straightforward to use within Kubernetes environments.
Cons of Cri-o
Kubernetes Dependency: Cri-o is tailored specifically for Kubernetes, so it may not be as versatile outside Kubernetes clusters.
Limited Features: Similar to Containerd, Cri-o lacks some of the comprehensive features available in Docker.
Also Read: Kubernetes (K8s) vs K3s
Containerd vs Docker vs Cri-o - Summary
Frequently Asked Questions
Can I run Docker images with containerd?
Yes, you can run Docker images with Containerd. Containerd is fully compatible with Docker images.
When did Docker start using containerd?
Docker started using Containerd in 2016
What is the difference between runC and Containerd?
runC is a lightweight container runtime, while containerd is a higher-level container runtime that manages the entire container lifecycle. runC is a component used by containerd to execute containers.
Does Kubernetes still use Docker?
As of Kubernetes version 1.20 and onwards, Kubernetes no longer requires Docker as its default container runtime.
Is containerd better than Docker?
Containerd is often considered better for resource optimization and performance. In contrast, Docker is preferred for its comprehensive features and user-friendly interface.