Docker-compose Build Args in docker-compose.yaml

We can make the docker-compose file more generic by passing a build argument to it.

contents of app.py

import os
import time
import redis
from flask import Flask


app = Flask(__name__)
cache = redis.Redis(host='redis', port=6379)

def get_hit_count():
    retries = 5
    while True:
        try:
            return cache.incr('hits')
        except redis.exceptions.ConnectionError as exc:
            if retries == 0:
                raise exc
            retries -= 1
            time.sleep(0.5)
@app.route('/')
def hello():
    count = get_hit_count()
    return 'Hello World! I have been seen {} times.\n'.format(count)
if __name__ == "__main__":
    app.run(host="0.0.0.0")

contents of requirements.txt

flask
redis

contents of docker-compose.yaml. let's understand the argument along with other options in the docker-compose file.

version: '3'
services:
  web:
    build:
      context: .
      dockerfile: Dockerfile
      args:
        - PYTHON_VERSION=3.4
    image: python-redis-2
    ports:
     - "5000:5000"
  redis:
    image: "redis:alpine"

Context : It is used to specify the directory where the docker file resides.

Dockerfile: Specifies the name of the docker file.

Args: It is the main parameter that will specify the python version, which Dockerfile should read and use it accordingly.

Image: It is the same as explained earlier.

Docker file:

#FROM python:3.4-alpine
ARG PYTHON_VERSION
FROM python:$PYTHON_VERSION
ADD . /code
WORKDIR /code
RUN pip install -r requirements.txt
CMD ["python", "app.py"]

Here, in the above docker file ARG PYTHON_VERSION is the parameter which the docker file will read from docker-compose file and based on it,it will use the python image.

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