Container Image

A container image is a lightweight, standalone, executable package that includes everything needed to run an application - the code, runtime, system tools, libraries and settings. Images become containers at runtime. Images are immutable, meaning they don't change once created.

Container images are created from a Dockerfile, which is a text file containing instructions for how to build the image. For example, a Dockerfile could start from a base image like Ubuntu, then run apt commands to install dependencies, copy over the application code, and define a command to run on start up. Images are stored in registries like Docker Hub and can be downloaded to local machines or cloud servers to start containers. Multiple containers can share the same image and run as isolated instances. Images are identified by tags that indicate the image name and version. Overall, container images allow applications to be packaged up with all dependencies into a standardized unit for consistent deployment across environments.