The article explores the differences and complementary features of Docker and containerd, two key technologies in the containerization ecosystem. Docker, launched in 2013, revolutionized container technology by simplifying application packaging, distribution, and execution in isolated environments, while containerd, initially a component of Docker, became a standalone container runtime in 2016, emphasizing simplicity, robustness, and portability. The piece explains how containerd functions as the underlying runtime for Docker, providing essential operations like image management and resource allocation, and discusses its interoperability with Kubernetes through the Container Runtime Interface (CRI). Docker, aimed at improving user experience, offers additional features such as easier container management and image building, making it more suitable for development and CI environments, whereas containerd is better suited for production and resource-constrained environments. The article also highlights Docker's networking capabilities, Docker Compose for multi-container applications, and how both technologies can be effectively used together, especially in production setups where orchestration systems like Kubernetes are employed.