Docker Workshop 3

app.py

#!/usr/bin/env python3
from flask import Flask
import os
import redis
import time

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


class EnvNotSetError(Exception):
    def __repr__(self):
        return "EnvNotSetException was raised."
    pass


def getHitCount():
    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)


def getMessage():
    configfile = os.getenv("APPCONFIG")
    if not configfile:
        raise EnvNotSetError()
        
    with open(configfile, "r") as f:
        lines=[x[8:].strip() for x in f.readlines() if x.startswith("Message=")]

    return lines[0]


@app.route("/")
def index():
    try:
        message = getMessage()
    except FileNotFoundError:
        message = "CONFIGURATION FILE NOT FOUND! THIS IS NOT OK!"
    except IndexError:
        message = "CONFIGURATION FILE FOUND BUT NO MESSAGE! THIS IS NOT OK!"
    except EnvNotSetError:
        message = "ENVIRONMENT VARIABLE NOT SET! THIS IS NOT OK!"
    except Exception as ex:
        message = f"BIG ERROR: {ex}"

    count = getHitCount()

    return f"Hello! I have a Message for you. It reads:\n\n{message}\n\nI have seen you {count} times!"

app.run(host="0.0.0.0", port=3000, debug=True)

docker-compose.yml

version: "3.9"
services:
  web:
...
build from here, mount volumes, set environments, set ports, 
...
  redis:
    image: "redis:alpine"

Dockerfile

FROM python:3.7-alpine
RUN apk add --no-cache gcc musl-dev linux-headers

...add files, set env, install stuff, etc...

RUN pip install -r requirements.txt

...add files, set env, install stuff, etc...

CMD python app.py

requirements.txt

flask
redis