docker / cli

Plugins and Extensions

The Docker CLI offers a flexible plugin system that enables users to extend its functionality. This outline explores the structure and capabilities of plugins within the Docker CLI.

Overview

Plugins are external programs that integrate with the Docker CLI, offering additional commands and features. They are designed to be modular and reusable, allowing developers to extend the Docker CLI’s capabilities without modifying the core codebase.

Plugin Structure

Plugins follow a specific structure, conforming to the following conventions:

  • Plugin Name: The plugin’s name is used as the command prefix within the Docker CLI.
  • Plugin Entry Point: The plugin’s entry point is a script that handles command execution and communication with the Docker CLI.
  • Plugin Configuration: Plugins can utilize configuration files to define their settings and behavior.

Plugin Development

Developing a plugin for Docker CLI involves the following steps:

  1. Define the Plugin Name and Command: Choose a descriptive name for your plugin and determine the commands it will provide.
  2. Create the Plugin Entry Point: Write a script (typically using Go or Bash) that defines the plugin’s logic and interacts with the Docker CLI.
  3. Handle Plugin Configuration: If necessary, create configuration files to store settings and parameters.
  4. Register the Plugin: Install the plugin into the Docker CLI’s plugin directory or use the docker plugin install command.

Integrating Plugins with Docker CLI

Plugins interact with the Docker CLI through a well-defined communication protocol. This protocol utilizes standard input/output (stdin/stdout) for data exchange and environment variables for passing contextual information.

Plugin Examples

  1. Docker Compose Plugin: The docker-compose plugin integrates the functionality of Docker Compose into the Docker CLI.
  2. Docker Swarm Plugin: The docker-swarm plugin provides commands for managing and interacting with Docker Swarm clusters.

Plugin Directory Structure

The Docker CLI utilizes the cli-plugins directory to store and manage installed plugins. The directory contains subdirectories for each plugin, with the plugin’s entry point script located within the main directory.

Conclusion

The Docker CLI’s plugin system provides a powerful mechanism for extending its capabilities. By leveraging this system, developers can create custom commands and features, enhancing the user experience and addressing specific use cases.