Construct Of An Docker Image And Its Building Process
A Docker image is like a box of Oreo. Its final image is like multiple Oreos (layer) stacked on top of each other. A layer could be built from multiple building stages (like our favorite chocolate topping), and each stage consists of smaller layers.
Now Let’s walk through a basic example
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# Stage 0: Build Stage
FROM node:18-alpine AS build
WORKDIR /app
COPY package*.json ./
RUN npm install --production
COPY . .
RUN npm run build
# Stage 1: Final Stage
FROM node:18-alpine
WORKDIR /app
COPY --from=build /app/dist ./dist
CMD ["node", "dist/main.js"]
Layers: Docker images are built in layers.
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WORKDIR /app
COPY package*.json ./
RUN npm install --production
- Each layer is an instruction such as
RUN,COPY,ADD, etc. Each layer is stacked on top of each other. The above is a three-layer model.
Stages: The above is a two layer build. Each stage starts from a FROM command, which launches a base image.
- Stage 0 creates artifacts / build of the custom app (e.g.,
RUN npx run build). It consists of several layers -
Stage 1 is created by launching a new base image
node:18-alpineand copying the build artifacts from Stage 0. The final image only contains layers from the last stage and files copied from previous stages. So Stage 0 is effectively discarded. - To use a custom Dockerfile, use the
-farg:docker build -f Dockerfile_test_container . -t ros-noetic-simple-robotics-tests
Create An Entrypoint
An entrypoint is a script that runs once a container starts. Here, we need to copy the entry point to a common location, then execute it
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COPY entrypoint_rgbd_slam_docker.sh /entrypoint_rgbd_slam_docker.sh
# RUN chmod +x /entrypoint_rgbd_slam_docker.sh
ENTRYPOINT ["/entrypoint_rgbd_slam_docker.sh"]
# must follow ENTRYPOINT, otherwise the container won't execute bash
CMD ["bash"]
In entrypoint, make sure the last line has
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...
# Execute the CMD command (bash) by replacing the shell with the CMD command in Dockerfile
exec "$@"
Changing Python Version to Python 3.10 (Not Recommended For Potential Code Breaking)
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# Add Deadsnakes PPA and install Python 3.10
RUN apt-get update && apt-get install -y software-properties-common && \
add-apt-repository ppa:deadsnakes/ppa && \
apt-get update && \
apt-get install -y python3.10 python3.10-dev python3.10-venv python3.10-distutils && \
rm -rf /var/lib/apt/lists/*
# Install pip for Python 3.10
RUN wget https://bootstrap.pypa.io/get-pip.py && \
python3.10 get-pip.py && \
rm get-pip.py
# Update alternatives to set python3 to python3.10
RUN update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.8 1 && \
update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.10 2 && \
update-alternatives --set python3 /usr/bin/python3.10
# Set environment variables for Python
ENV PYTHON_VERSION=3.10
ENV PYTHON_BIN=/usr/bin/python${PYTHON_VERSION}
ENV PIP_BIN=/usr/local/bin/pip
# Upgrade pip and setuptools, then install a compatible PyYAML version
RUN pip3 install --upgrade pip setuptools wheel && \
pip3 install --force-reinstall --ignore-installed PyYAML==6.0
