Creating an Event Function Using a Container Image Built with Python

For details about how to use a container image to create and execute an event function, see Creating an Event Function Using a Container Image and Executing the Function. This section describes how to create an image using Python and verify the image locally.

1. Run the following command to create an empty folder named custom_container_event_example:

   mkdir custom_container_event_example && cd custom_container_event_example

2. Use Python to implement an HTTP server to process init and invoke requests and send responses.

   Run the following command to create a main.py file:

   touch main.py

   Introduce the Flask framework in the code and implement a function handler (method POST and path /invoke) and an initializer (method POST and path /init). Here is the code for main.py:

   import json
   
   from flask import Flask, request
   
   # Create a Flask application instance.
   app = Flask(__name__, template_folder='templates', static_folder='static')
   
   # Define the initialization API.
   @app.route('/init', methods=['POST'])
   def init():
       # Print the request path for debugging.
       print("***" + request.path + "***", flush=True)
   
       # Build response data.
       data = {
           "statusCode": 200,
           "isBase64Encoded": False,
           "body": json.dumps("init successes"),
           "headers": {
               "Content-Type": "application/json"
           }
       }
       return json.dumps(data)
   
   # Define the API.
   @app.route('/invoke', methods=['POST'])
   def invoke():
       print("***" + request.path + "***", flush=True)
       data = {
           "statusCode": 200,
           "isBase64Encoded": False,
           "body": json.dumps("invoke successes"),
           "headers": {
               "Content-Type": "application/json"
           }
       }
       return json.dumps(data)
   
   # Main program entry
   if __name__ == '__main__':
       app.run(host="0.0.0.0", port=8000)

3. Create a Dockerfile.

   touch Dockerfile

   The content of Dockerfile is as follows:

   FROM ubuntu:22.04
   
   ENV HOME=/home/custom_container
   ENV GROUP_ID=1003
   ENV GROUP_NAME=custom_container
   ENV USER_ID=1003
   ENV USER_NAME=custom_container
   
   RUN mkdir -m 550 ${HOME} && groupadd -g ${GROUP_ID} ${GROUP_NAME} && useradd -u ${USER_ID} -g ${GROUP_ID} ${USER_NAME}
   
   RUN apt-get update &&  \
       apt-get install -y --no-install-recommends python3 pip &&  \
       apt-get clean
   
   RUN pip3 install --verbose flask jsons requests --no-cache-dir
   
   COPY main.py ${HOME}
   
   RUN chown -R ${USER_ID}:${GROUP_ID} ${HOME}
   RUN chmod -R 775 ${HOME}
   
   USER ${USER_NAME}
   WORKDIR ${HOME}
   EXPOSE 8000
   ENTRYPOINT ["python3", "main.py"]

   Table 1 Instructions

   Instruction	Description
   FROM	Specifies base image ubuntu:22.04. The base image is mandatory and its value can be changed.
   ENV	Sets environment variables HOME (/home/custom_container), GROUP_NAME and USER_NAME (custom_container), and USER_ID and GROUP_ID (1003). These environment variables are mandatory and their values can be changed.
   RUN	Executes commands. The format is RUN <command>. For example, RUN mkdir -m 550 ${HOME} means to create directory ${HOME} for user ${USER_NAME} during container building.
   COPY	Copies files or directories from the build context to the image. Copy main.py to the ${HOME} directory of user ${USER_NAME} in the container.
   USER	Switches to user ${USER_NAME}.
   WORKDIR	Switches the working directory to the ${HOME} directory of user ${USER_NAME}.
   EXPOSE	Informs Docker that the container listens on the specified network ports at runtime. Expose port 8000 of the container and do not change it.
   ENTRYPOINT	Sets the executable command that is run each time a container starts. Run the python3 main.py command to start a container.

4. Run the following command to build an image:

   docker build -t custom_container_event_example:latest .

   In the preceding command, the image name is custom_container_event_example, the tag is latest, and the period (.) indicates the directory where the Dockerfile is located. Run the image build command to pack all files in the directory and send the package to a container engine to build an image.