21 Days of Docker-Day 17 -Building Effective Docker Image

Welcome to Day 17 of 21 Days of Docker. The topic for today is the Building Effective Docker Image.

What are the containers layers?

On Day 8, I talked about Docker Images and layers.

21 Days of Docker-Day 8-Docker Images, Layers & Containers

Image is build of a bunch of image layers and when we boot the container using this image, container adds a read-write layer on the top of it.

Now at this stage, the question you need to ask yourself, why do I care how many layers I have?

• More layers mean a larger image. The larger the image, the longer it takes to both build, push and pull from the registry.
• Smaller images mean faster builds and deploys.

How can I reduce my layers?

• Use shared base images where possible.
• Limit the data written to the container layer.
• Chain RUN statements
• Prevent cache misses at build for as long as possible.

Other steps we can do, to build an optimized image

Choosing the right base image

centos                                                                                  latest              9f38484d220f        7 months ago        202MB

vs

python                                                                                  3.7.3-alpine        2caaa0e9feab        3 months ago        87.2MB

• In this case, if I am building a Python application, I don’t need entire centos operating, I just need a minimal base OS(which is provided by alpine), with all the Python binaries installed on the top of it.

FROM ubuntu:latest  --> FROM python:3.7.3-alpine
LABEL maintainer="laprashant@gmail.com"
RUN apt-get update -y && \-->we don't need this as Python image already include it
    apt-get install -y python-pip python-dev
COPY ./requirements.txt /app/requirements.txt
WORKDIR /app
RUN pip install -r requirements.txt
COPY . /app
ENTRYPOINT [ "python" ]
CMD [ "app.py" ]

To read the complete blog

21 Days of Docker-Day 17 -Building Effective Docker Image

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