Image layers concept in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Docker image layer?

A Docker image layer is a read-only file system change that represents a step in the image build process. Layers stack on top of each other to form the final image.

beginner

How do Docker image layers help with efficiency?

Docker image layers allow reusing unchanged layers across images, saving disk space and speeding up downloads and builds.

intermediate

What happens if you change a file in a Docker image layer?

A new layer is created with the change. The previous layers remain unchanged and are reused if possible.

intermediate

Why is the order of commands in a Dockerfile important for image layers?

Because each command creates a new layer, ordering commands to minimize changes in early layers helps reuse cached layers and speeds up builds.

beginner

Can you modify a Docker image layer after it is created?

No, Docker image layers are immutable. Changes create new layers on top of existing ones.

What does each Docker image layer represent?

A A network configuration

B A running container

C A change or instruction in the Dockerfile

D A user session

Each layer corresponds to a Dockerfile instruction that changes the image.

Why are Docker image layers immutable?

A To allow caching and reuse of layers

B To allow editing layers directly

C To prevent image creation

D To slow down builds

Immutability allows Docker to cache and reuse layers efficiently.

What happens if you reorder commands in a Dockerfile?

A It has no effect

B It deletes all layers

C It changes the container runtime

D It can affect build speed and cache usage

Reordering commands can improve or reduce cache reuse, affecting build speed.

How does Docker save disk space with image layers?

A By sharing unchanged layers between images

B By deleting old images automatically

C By compressing containers

D By running fewer containers

Docker shares layers that are the same across images to save space.

If you change a file in a Docker image, what does Docker do?

A Modifies the existing layer

B Creates a new layer with the change

C Deletes the image

D Restarts the container

Docker adds a new layer on top with the file change; existing layers stay unchanged.

Explain how Docker image layers work and why they are important.

Think about how changes in a Dockerfile create layers and how Docker uses them.

Describe the impact of Dockerfile command order on image layers and build efficiency.

Consider how Docker caches layers and how changing commands affects this.