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Chapter 6: Why Docker, Images and How a Container Is Created

6.3 Image vs container

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Word Meaning Picture
Image Read-only template. Built or pulled. Has a name and a tag. Sealed runnable template
Container A running or stopped process created from an image, plus a writable layer One process from that template
Layer A filesystem diff from one Dockerfile step One prep step frozen in the kit
Registry Stores images (Docker Hub is the lab registry) The shelf operations pulls from 
  Dockerfile --build--> Image --run--> Container
                              ^
                         pull from a registry

Many containers can come from one image. docker rm removes a container. The image stays until docker rmi.

docker version

What you see when it works: a Client block and a Server (Engine) block, each with a version. If the client exists but the server errors, the daemon is not running. Start Docker Desktop on Windows or Mac, or start the engine on Linux, then run docker version again.

Install from Docker's own docs or Docker Desktop. Package names change. This chapter does not freeze an apt or yum line.

Practice task

Which command creates an image, and which creates a container? One sentence on why deleting the container does not delete the image.

Ravi Sir's Cards for this lesson

Image vs container. These two words are mixed up in almost every beginner question.Revision cardWhat is the difference between an image and a container? Image: read-only package. Container: a running copy with a small writable layer.Interview cardDocker image vs Docker container. Docker packs an app with everything it needs so it runs the same everywhere.Image: a read-only package (app + libraries + settings). Like a recipe.Container: a runninComparison card

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