docker start a web container

Step 1: Setup

Define the application dependencies.

1. Create a directory for the project:

   mkdir web
   cd web
   

2. Create a file called app.py in your project directory and paste this in:

   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)
   

3. Create another file called requirements.txt in your project directory and paste this in:

   flask
   redis
   

Step 2: Create a Dockerfile

In this step, you write a Dockerfile that builds a Docker image. The image contains all the dependencies the Python application requires, including Python itself.

In your project directory, create a file named Dockerfile and paste the following:

# syntax=docker/dockerfile:1
FROM python:3.7-alpine
WORKDIR /code
ENV FLASK_APP=app.py
ENV FLASK_RUN_HOST=0.0.0.0
RUN apk add --no-cache gcc musl-dev linux-headers
COPY requirements.txt requirements.txt
RUN pip install -r requirements.txt
EXPOSE 5000
COPY . .
CMD ["flask", "run"]

Step 3: Define services in a Compose file

Create a file called docker-compose.yml in your project directory and paste the following:

version: "3.9"
services:
  web:
    build: .
    ports:
      - "8000:5000"
  redis:
    image: "redis:alpine"

Step 4: Build and run your app with Compose

From your project directory, start up your application by running docker compose up.