# 1. Start a redis container
docker run -d -p 6379:6379 redis
        

# 2. Create a Flask app
# app.py
import os
import time
import redis
from flask import Flask

def get_ip():
    """Receive hostname by an environment variable or using localhost
    """
    return os.getenv('MYREDIS_HOST', 'localhost')

app = Flask(__name__)
cache = redis.Redis(host=get_ip(), 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 from Docker! I have been seen {} times.\n'.format(count)

if __name__ == '__main__':
    app.run(debug=True, port=8080) # set up debug to be True to hot reload
        

# 3. Run the app
python app.py
        

http://localhost:8080/
        

# app.py
import os
import time
import redis
from flask import Flask

def get_ip():
    return os.getenv('MYREDIS_HOST', 'localhost')

app = Flask(__name__)
cache = redis.Redis(host=get_ip(), 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 from Docker! I have been seen {} times.\n'.format(count)

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)
        

# Dockerfile
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 ["python", "app.py"]
		

# Developer Side

# 1. Create the dependent package list
pip freeze > requirements.txt

# 2. Create an image docker.io/library/lchenlangley/count
# lchenlangey is the account at Docker Hub
docker build -t lchenlangley/count .

# 3. Push the image to Docker Hub, each organizaiton may have their own private image registry
docker login
docker push lchenlangley/count
        

# Deployment on Host

# 1. Create a bridge network
docker network create asgard

# 2. Create a redis container named as redisserver
docker run -d --name redisserver --network asgard redis

# 3. Create a container for the app
# Pass redis container name to the app with an environment variable
docker run -d --network asgard -e MYREDIS_HOST=redisserver -p 8000:5000 lchenlangley/count
        

# User Side
http://localhost:8000/
		

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