A Docker registry is a service that stores and distributes container images. Images are organized into repositories, and the registry serves manifests and blobs: the manifest describes what to pull, while blobs hold image layers and configuration data. In practice, a registry is the supply chain for containers, whether it is public or private.
In cyber security, registries matter because they can expose more than software. Old layers, cached build files, environment variables, and embedded credentials may remain in image history. If a registry is left public or misconfigured, attackers can enumerate repositories, pull manifests, and inspect blobs to harvest secrets or steal proprietary images. Defenders reduce this risk by requiring authentication, using TLS, restricting network access, scanning images before publication, and rotating any keys found in exposed layers. A secure registry helps prevent container distribution from becoming a secret archive.