Docker daemon

Docker daemon, aslo people call it Docker Server,operates silently in the background of the hosting system, orchestrating Docker elements such as images, containers, networks, and storage volumes. Users typically don't engage with the daemon directly; they interact through the Docker client using commands or alternative tools that communicate with the daemon via RESTful APIs, socket connections, or command-line inputs.

Key Responsibilities of the Docker Daemon

Image Creation and Management: The daemon enables the crafting of Docker images, as well as their dissemination and retrieval from external repositories, notably Docker Hub.

Container Lifecycle Management: The daemon plays a pivotal role in instantiating containers from Docker images and supervising their various states throughout their lifecycle.

Network Configuration and Management: It has the capability to structure and streamline the network interactions both within containers and between the containers and the host environment.

Volumes and Persistence Handling: The daemon is crucial in managing the persistent storage aspect of Docker, facilitating the segregation of a container’s data away from its runtime lifecycle.

Initiating the Docker Daemon

One can initialize the Docker Server by deploying the `dockerd` command. Configuration of the daemon can be refined using a combination of command-line flags or by specifying preferences in a configuration file. The customization allows for adjusting various operational facets such as network configurations, security measures, data and log storage pathways, and the setup for clustered operations using features like Docker Swarm.

These core functionalities underscore the Docker daemon's integral role in the containerized ecosystem, providing the necessary mechanisms for a secure, stable, and efficient Docker experience.

Engaging with the Docker Daemon

Several methods are available for interfacing with the Docker Server including:

Docker CLI: The primary method for most is utilizing the CLI to send commands to the Docker Server.

Remote API Access: Direct interaction with the daemon is facilitated using HTTP or HTTPS requests through Docker's API, offering a programmatic way to control Docker operations.

Graphical User Interfaces and External Utilities: A range of GUIs and tools developed by third parties enhance the ease of managing Docker, visually displaying containers and associated services.

Safety

Securing the Docker daemon is crucial given its role in handling Docker entities like images and containers and the possibility of executing code on the host system with elevated privileges. Implementing robust security measures for the daemon and its operational environment is of paramount importance. Key aspects to consider in the security strategy for the Docker daemon include:

Daemon Authentication: The Docker daemon is configured to only accept local connections through Unix sockets by default, which limits access to users on the host system. For instances where remote access is necessary via a TCP socket, it is advised to employ TLS with rigorously set up and authenticated certificates to ensure encrypted communication and proper client verification.

Privilege Restriction: Running the Docker daemon and containers with the lowest possible privileges reduces security risks. This means that you cannot use superuser accounts for containers unless absolutely necessary.

Using AppArmor or SELinux rules: these tools help to limit the capabilities that processes have, including for the Docker daemon. They allow you to create security policies that control how applications can interact with the system.

Limiting the use of kernel capabilities: Linux kernels allow detailed control over the privileges of processes. Docker can run containers with a limited set of privileges so that the container does not have full access to system capabilities.

Isolation of resources: The use of cgroups (control groups) in Linux allows Docker to limit how much system resources (CPU, memory, etc.) a container can use, which helps prevent DoS attacks.

New updates and patching: Regular updating of Docker and the host system is important to close known security vulnerabilities. It should be ensured that the latest software versions are used and all necessary security patches are installed.

Logging and auditing: Continuous monitoring and analysis of daemon and container logs can be used to detect suspicious activity or other indicators of compromise.

Image Security: It is important to ensure that the Docker images used are obtained from trusted sources and kept up to date in a secure state.

Network Access Restriction: Managing inbound and outbound connections to containers and restricting access between containers helps minimize the risk of attack propagation.

Using these and other security practices helps secure the Docker daemon and containers, reducing the risk of potential threats and attacks.

Versioning the Docker Daemon

Docker is updated quite frequently, bringing new features, fixes, and security improvements. Each version has its own unique number that follows the versioning semantics (MAJOR.MINOR.PATCH). For example, in version 20.10.5, 20 is the major version number (major), 10 is the minor version number (minor), and 5 is the patch number (patch). Docker tries to follow the principle of backward compatibility, which makes it easier to upgrade to new versions.

Updating

It is recommended that you regularly update Docker to the latest versions to improve system security and performance. Updating Docker may require stopping the daemon, executing the update command, and restarting the system. For large production systems, updates should be carefully planned, tested in bench environments first, and follow appropriate documentation to minimize downtime and other potential risks.

Architectural features

Docker operates on a client-server model in which the client interfaces with the daemon (the server component) through a RESTful API. This architecture permits the Docker daemon to be platform-agnostic, enabling the use of Docker across varied operating systems and cloud environments.

Orchestration System Integration

The Docker daemon seamlessly integrates with orchestration platforms, providing the ability to scale, deploy, and manage services across distributed systems effectively.

Docker Daemon performance

Daemon performance can be optimized by tweaking configuration files and using resource management best practices. For example, limiting the excessive number of containers running simultaneously can help prevent excessive resource consumption and improve overall system performance.

Learn Docker with Serverspace

Serverspace has Docker FAQ page where you can find a lot of information about docker:
from Docker Engine to Basic Docker commands.

Also Serverspace has article - Docker for begginers that can serve you as "gate" to the world of that open platform.