Choosing small base images (alpine, slim) in Docker - Commands & Configuration

Introduction

Large container images take longer to download and use more disk space. Choosing small base images like alpine or slim helps make your containers lightweight and faster to start.

When you want your application containers to start quickly on any machine.

When you have limited disk space on your server or developer machine.

When you want to reduce network bandwidth usage during deployments.

When you want to improve security by minimizing the software inside your container.

When you want to speed up your continuous integration and delivery pipelines.

Config File - Dockerfile

Dockerfile

FROM python:3.11-slim

WORKDIR /app

COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

COPY . .

CMD ["python", "app.py"]

FROM python:3.11-slim uses a smaller Python base image with fewer extra tools to keep the image size small.

WORKDIR /app sets the working directory inside the container.

COPY requirements.txt . copies the dependency list.

RUN pip install --no-cache-dir -r requirements.txt installs dependencies without caching to reduce image size.

COPY . . copies the application code.

CMD runs the app.

Commands

Builds the Docker image named 'my-python-app' using the Dockerfile in the current directory.

Terminal

docker build -t my-python-app .

Expected Output

Sending build context to Docker daemon  12.34MB

Step 1/6 : FROM python:3.11-slim

3.11-slim: Pulling from library/python

Digest: sha256:...

Status: Downloaded newer image for python:3.11-slim

 ---> abcdef123456

Step 2/6 : WORKDIR /app

 ---> Running in 123abc456def

Removing intermediate container 123abc456def

 ---> 789def012345

Step 3/6 : COPY requirements.txt .

 ---> 456abc789def

Step 4/6 : RUN pip install --no-cache-dir -r requirements.txt

 ---> Running in 789abc123def

Collecting flask

Installing collected packages: flask

Successfully installed flask-2.3.2

Removing intermediate container 789abc123def

 ---> 012def345abc

Step 5/6 : COPY . .

 ---> 345abc678def

Step 6/6 : CMD ["python", "app.py"]

 ---> Running in def123abc456

Removing intermediate container def123abc456

 ---> 678def901abc

Successfully built 678def901abc

Successfully tagged my-python-app:latest

Shows the size and details of the built image to verify it is small.

Terminal

docker images my-python-app

Expected Output

REPOSITORY      TAG       IMAGE ID       CREATED          SIZE

my-python-app   latest    678def901abc   10 seconds ago   120MB

Runs the container to check the Python version and confirm the image works as expected.

Terminal

docker run --rm my-python-app python --version

Expected Output

Python 3.11.4

→

--rm - Automatically removes the container after it exits to keep your system clean.

Key Concept

If you remember nothing else from this pattern, remember: using small base images like alpine or slim makes your containers faster and lighter.

Common Mistakes

Using the full base image like 'python:3.11' instead of 'python:3.11-slim' or 'alpine'.

Full images include many extra tools and libraries, making the container large and slow to download.

Choose 'slim' or 'alpine' tags for base images to keep your container size small.

Not using '--no-cache-dir' when installing packages inside the container.

Pip caches installation files which increase the image size unnecessarily.

Always use 'pip install --no-cache-dir' to avoid caching and reduce image size.

Copying unnecessary files into the container increasing image size.

Extra files add to the image size and can slow down builds and deployments.

Use a .dockerignore file to exclude files not needed in the container.

Summary

Use small base images like alpine or slim to reduce container size and speed up startup.

Build your Docker image and check its size with 'docker images' to confirm it is small.

Run your container with '--rm' to test it and keep your system clean.