app.py

from flask import Flask
from redis import Redis, RedisError
import os
import socket

# Connect to Redis
redis = Redis(host="redis", db=0, socket_connect_timeout=2, socket_timeout=2)

app = Flask(__name__)


@app.route("/")
def hello():
    try:
        visits = redis.incr("counter")
    except RedisError:
        visits = "<i>cannot connect to Redis, counter disabled</i>"

    html = "<h3>Hello {name}!</h3>" \
           "<b>Hostname:</b> {hostname}<br/>" \
           "<b>Visits:</b> {visits}"
    return html.format(name=os.getenv("NAME", "world"), hostname=socket.gethostname(), visits=visits)


if __name__ == "__main__":
    app.run(host='0.0.0.0', port=80)

"""
the app prints the environment variable NAME,
as well as the output of a call to socket.gethostname().
Finally, because Redis isn't running
(as we've only installed the Python library, and not Redis itself),
we should expect that the attempt to use it here will fail and produce the error message.
"""