Docker images
Docker images are the building blocks of Docker containers. An image is essentially a lightweight, portable, and self-contained package that contains all the necessary files, libraries, and configurations needed to run a Docker container. Images are created using a Dockerfile, which is a text file that contains a set of instructions for building the image.
Here's an example of a simple Dockerfile that creates an image for a Python application:
FROM python:3.9
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
CMD ["python", "app.py"]
This Dockerfile specifies that the image should be based on the official Python 3.9 image from Docker Hub. It then sets the working directory to /app, copies the requirements.txt file into the container, installs the required packages using pip, copies the entire application directory into the container, and finally sets the command to run the app.py file.
To build the image, you can run the following command in the directory where the Dockerfile is located:
docker build -t my-python-app .
This will create an image called my-python-app with the current directory as the build context. The -t option specifies the name and optional tag for the image.
To pull an existing image from a remote registry, such as Docker Hub, you can use the docker pull command:
docker pull nginx:latest
This command pulls the latest version of the official Nginx image from Docker Hub.
To push an image to a remote registry, you first need to tag the image with the repository and tag that you want to use. For example:
docker tag my-python-app my-username/my-python-app:latest
This tags the my-python-app image with the repository name my-username/my-python-app and the tag latest. Finally, you can push the image to the remote registry using the docker push command:
docker push my-username/my-python-app:latest
This uploads the my-python-app image to the Docker Hub registry under the my-username/my-python-app repository with the latest tag.
In summary, Docker images are self-contained packages that contain all the necessary files and configurations needed to run a Docker container. You can create images using a Dockerfile, pull images from a remote registry, and push images to a remote registry using the docker build, docker pull, and docker push commands.
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