Explain Docker registry and how to set up a private registry.

Docker registry is a storage and distribution system for Docker images. Types: 1) Docker Hub (public), 2) Private registries (self-hosted), 3) Cloud registries (AWS ECR, Google GCR, Azure ACR). Setting up private registry: docker run -d -p 5000:5000 --name registry registry:2, docker tag myapp localhost:5000/myapp, docker push localhost:5000/myapp, docker pull localhost:5000/myapp. Production setup includes TLS certificates, authentication with htpasswd, and persistent volumes. Authentication: htpasswd -Bbn username password > auth/htpasswd, docker login localhost:5000.