Packaging Applications as Docker Containers

Packaging Applications as Docker Containers Packaging applications as Docker containers can make deployment and management more convenient. Here is an example that demonstrates how to package a Python application as a Docker container and execute it using Docker Compose. Basic Template To containerize an application with Docker, you first need to ensure that Docker is installed. Then, you need to create these two files in the root directory of your Python application: Dockerfile and compose.yaml, which will roughly contain the following: ```Dockerfile title="Dockerfile" Set the base image to the official Python image, version can be customized FROM python:3.9 Set the working directory to /app WORKDIR /app Copy the dependency files of the Python application COPY requirements.txt . Install the application dependencies RUN pip install --no-cache-dir -r requirements.txt Copy the application files, copy from the current directory to the directory inside the container COPY . . Set the default command to execute CMD ["python", "app.py"] ``` yaml title="compose.yaml" version: "3" services: app: build: . In this compose.yaml file, we define a service named app. With the build: . instruction, it will use the Dockerfile file in the current directory to build the image. Run docker compose up in the directory of compose.yaml to build and start the application. Example: Packaging a Simple Python Application as a Docker Container Here is a simple Hello World application example, a Python application that prints Hello World on a webpage: python title="app.py" from flask import Flask app = Flask(__name__) @app.route("/") def hello(): return "Hello World!" if __name__ == "__main__": app.run(host="0.0.0.0", port=int("8000"), debug=True) If we deploy the Python application using the normal process without containerization, we need to install dependencies first. For some packages that need to be compiled and installed, errors may occur in the Windows environment, and necessary header files may be missing. If we package it as a Docker container, we can ignore the differences in the environment. Even if the host machine is not connected to the network, we only need to copy the image to complete the deployment. The following steps show how to containerize it with Docker and deploy it with Docker Compose. First, create a file named Dockerfile and fill in the following: ```Dockerfile title="Dockerfile" Set the base image to the official Python image FROM python:3.9 Copy the application files COPY . /app Set the working directory WORKDIR /app Install dependencies RUN pip install flask Expose port 8000 for access EXPOSE 8000 Start the application CMD python ./app.py ``` Then, create a file named compose.yaml in the same directory and copy the following content: yaml title="compose.yaml" version: "3" services: helloworld-flask: build: . ports: - "8099:8000" # Port 8099 can be customized Now, you can open the terminal, go to the directory containing the Dockerfile and compose.yaml files, and run the following command to start the application: shell docker compose up Docker will build an image and start a container. Accessing http://localhost:8099 will display the characters "Hello World". By following these steps, a simple Python application can be containerized and deployed using Docker Compose. References and Acknowledgements Containerize an application Containerize a Python application in 3 minutes This post is translated using ChatGPT, please feedback if any omissions.