如何挂载 Docker 容器卷

Question

My requirement is like this:

Q) I have a little python app running a small flask server on a docker container. I need to pass a value to this container that will return from the python server. but I need to change this passing value occasionally and I DON'T WANT TO build the image every time I do a change to this passing value.

For this what I have done this set .env file and set the environment variables I need to pass like below:

this is my .env :

MY_NAME=John McBeth

This is my server.py :

from flask import Flask
app = Flask(__name__)
import os

PORT = 8083

return_value = os.environ(['MY_NAME']) # value I am getting from .env

@app.route('/')
def hello_world():
    return str(return_value)

if __name__ == '__main__':
   app.run(host='0.0.0.0', port=PORT)

And I am building this from a docker-compose.yaml as below:

version: "3.2"

services:
  backend: 
    build: ./backends/banuka
    environment:
      CHOKIDAR_USEPOLLING: "true"
      MY_NAME: ${MY_NAME} // this is where I am passing the value in `.env`   
    ports: 
      - 8080:8083

PROBLEM: How can I set a volume to this container, that every time I change this name in .env it will reflect right after without building the image again and running?

Answer 1

Change your docker-compose.yml to:

version: "3.2"

services:
  backend: 
    build: ./backends/banuka
    volumes:
      - .:/path/to/project
    environment:
      CHOKIDAR_USEPOLLING: "true"
    env_file:
      - .env
    ports: 
      - 8080:8083

You can set /path/to/project to whatever you prefer, this will be the path inside your container, the . before only means current directory, which I suppose is the root directory of your project, you can change this too to any path in your machine you'd like to mount.

Also, you can set the .env file directly in compose with env_file option, which is what I actually recommend

https://docs.docker.com/compose/environment-variables/#the-env_file-configuration-option

Answer 2

Create a file along with docker-compose.yml
echo "John McBeth" > file_with_env_content

Mount file in container.

version: "3.2"

services:
  backend: 
    build: ./backends/banuka
    volumes:
      - ./file_with_env_content:/opt/file_with_env_content
    environment:
      CHOKIDAR_USEPOLLING: "true"

    ports: 
      - 8080:8083

And Change you python script to read content from temp file.

from flask import Flask
app = Flask(__name__)
import os

PORT = 8083

#return_value = os.environ(['MY_NAME']) # value I am getting from .env
f = open("/opt/file_with_env_content", "r")
return_value = f.readline() # Write your logic to select any specific line or key value pair etc.
f.close()


@app.route('/')
def hello_world():
    return str(return_value)

if __name__ == '__main__':
   app.run(host='0.0.0.0', port=PORT)