A container image is a packaged, read-only template that includes your application code, runtime, libraries, and configuration. Images act as blueprints from which containers are launched. They are built using instructions in a Dockerfile or similar build definition. Each image contains layered filesystem components, making distribution and versioning efficient.
Why it matters
Container images allow consistent deployments across environments by packaging everything the application needs. They integrate with CI/CD workflows, support reproducibility, and make rollbacks safe by allowing older versions to be redeployed instantly.
Examples
A Node.js application packaged into an image and stored in a registry can be deployed into Kubernetes or a cloud-run environment. Images are covered in the lesson Writing Dockerfiles.