Reducing final image size by 80 percent in Docker - Step-by-Step Execution

Process Flow - Reducing final image size by 80 percent

Start with large base image

↓

Use smaller base image

↓

Remove unnecessary files

↓

Use multi-stage builds

↓

Copy only needed artifacts

↓

Build final smaller image

↓

Done

This flow shows how to reduce Docker image size by choosing smaller bases, cleaning files, and using multi-stage builds.

Execution Sample

Docker

FROM python:3.12-slim
WORKDIR /app
COPY . /app
RUN pip install -r requirements.txt
CMD ["python", "app.py"]

A simple Dockerfile using a slim Python base image to reduce image size.

Process Table

Step	Action	Image Size Impact	Resulting Image Size
1	Start with python:3.12 full image	Large base image (~900MB)	900MB
2	Switch to python:3.12-slim base image	Smaller base (~150MB)	150MB
3	Remove cache and temp files after install	Reduce ~20MB	130MB
4	Use multi-stage build to copy only needed files	Remove build dependencies (~50MB)	80MB
5	Final image built with only runtime files	Final cleanup	80MB

💡 Final image size reduced from 900MB to 80MB (~80% reduction)

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
Image Size (MB)	900	150	130	80	80

Key Moments - 3 Insights

Why does switching to a slim base image reduce size so much?

Because the slim base removes many unnecessary tools and files, as shown in step 2 of the execution_table where size drops from 900MB to 150MB.

How does multi-stage build help reduce image size?

Multi-stage builds let you copy only the final needed files, removing build tools and dependencies, as seen in step 4 where size drops from 130MB to 80MB.

Why remove cache and temp files after installing packages?

Removing cache frees up space that package managers use temporarily, reducing image size as shown in step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the image size after switching to the slim base image?

A 150MB

B 900MB

C 80MB

D 130MB

💡 Hint

Check the 'After Step 2' row in variable_tracker or step 2 in execution_table.

At which step does the image size first drop below 100MB?

A Step 3

B Step 4

C Step 2

D Step 1

💡 Hint

Look at the 'Resulting Image Size' column in execution_table.

If you skip removing cache files after install, how would the image size after step 3 change?

A It would be smaller than 80MB

B It would increase to 900MB

C It would stay at 150MB

D It would be exactly 130MB

💡 Hint

Refer to step 3 in execution_table where removing cache reduces size from 150MB to 130MB.

Concept Snapshot

Docker image size can be reduced by:
- Using smaller base images like 'slim'
- Removing cache and temp files after installs
- Using multi-stage builds to copy only needed files
- Cleaning up unnecessary dependencies
This can reduce image size by around 80%.

Full Transcript

This lesson shows how to reduce Docker image size by starting with a large base image and switching to a smaller slim base. Then, removing cache and temporary files after package installation further reduces size. Using multi-stage builds copies only necessary files into the final image, removing build dependencies. Step by step, the image size drops from 900MB to 80MB, an 80% reduction. Key points include why slim images are smaller, how multi-stage builds help, and why cleaning cache matters. Visual quizzes test understanding of size changes at each step.