Diun is a Docker image update notifier written in Go that monitors container images across various platforms (Docker, Kubernetes, containerd, Nomad, Swarm, and file-based configurations) for updates. It periodically checks image manifests against a stored state (using BoltDB) and sends notifications via multiple channels (Slack, Telegram, email, etc.) when updates are detected. The application features a modular architecture with pluggable providers and notifiers, a gRPC interface for external interaction, Prometheus metrics, and structured logging. The system is designed for self-hosted environments to automate the detection of base image updates, application releases, and security rebuilds. Key components include a CLI for management, a scheduler for periodic checks, a template system for customizable notifications, and secret handling utilities. Diun's strength lies in its extensibility and wide platform support, making it a versatile tool for DevOps workflows.