Squashing layers in Docker - Mini Project: Build & Apply

Squashing Layers in Docker Images

📖 Scenario: You are working on a Docker project where you want to optimize the image size by combining multiple layers into one. This helps reduce the final image size and speeds up deployment.

🎯 Goal: Build a Dockerfile that creates a base image with multiple commands, then squash the layers into a single layer using Docker build options.

📋 What You'll Learn

Create a Dockerfile with multiple RUN commands

Add a label to the image

Use Docker build with the --squash option to combine layers

Display the final image size

💡 Why This Matters

🌍 Real World

Squashing layers helps reduce Docker image size, which saves storage and speeds up deployment in real projects.

💼 Career

Understanding layer squashing is important for DevOps roles to optimize container images and improve CI/CD pipelines.

1

Create a Dockerfile with base image and multiple RUN commands

Create a file named Dockerfile with the following content exactly: start from the alpine:latest image, then add two RUN commands: one to update the package list with apk update and another to install curl with apk add curl.

Docker

# Your code here

Need a hint?

Use FROM alpine:latest as the base. Then add two separate RUN lines for update and install.

2

Add a label to the Dockerfile

Add a LABEL instruction to the existing Dockerfile that sets maintainer to [e-mail].

Docker

FROM alpine:latest
RUN apk update
RUN apk add curl
# Add a LABEL instruction below

Need a hint?

Use LABEL maintainer="[e-mail]" exactly.

3

Build the Docker image with squashing layers

Use the Docker CLI to build the image from the current directory with the tag myapp:squashed and enable layer squashing using the --squash option.

Docker

FROM alpine:latest
RUN apk update
RUN apk add curl
LABEL maintainer="[e-mail]"
# Your code here

Need a hint?

Run docker build --squash -t myapp:squashed . in your terminal to build the image with squashed layers.

4

Display the final image size

Run the Docker command to show the size of the image tagged myapp:squashed.

Docker

FROM alpine:latest
RUN apk update
RUN apk add curl
LABEL maintainer="[e-mail]"
# Your code here

Need a hint?

Use docker images myapp:squashed to see the image size.