What is a container registry and which ones are commonly used?

A container registry is a repository for storing and distributing Docker images. After building a Docker image in CI, the pipeline pushes it to a registry; deployment systems then pull the image from the registry to run it. Common registries include: Docker Hub (the original public registry, free for public images), Amazon ECR (Elastic Container Registry, integrated with ECS and EKS, private), Google Artifact Registry / GCR (Google Cloud, integrated with GKE), GitHub Container Registry (GHCR) (tightly integrated with GitHub Actions), GitLab Container Registry, and Azure Container Registry (ACR). Private registries behind authentication ensure only authorized systems can pull production images. Versioning by git commit SHA (myapp:abc1234) allows precise traceability — you always know exactly which commit is running in production.