Cannot connect from python to influxdb when running in docker

Title is not entirely accurate, I'm open for suggestions!

You can find a full MCVE here: https://github.com/timstoop/20170614-python-docker-influxdb-problem

Tested with:

• docker-engine 17.05.0~ce-0~ubuntu-xenial
• docker-compose version 1.13.0, build 1719ceb

So the docker-compose starts an influxdb and a small python3 app. The only thing the app does is try to connect to influxdb, run a command and if that fails, wait 5 seconds and try again. If I run docker-compose up on this code, the app will never connect, it keeps retrying. These are the log lines it outputs:

app_1       | 2017-06-14 18:57:36.892955 ticker Trying InfluxDB connection...
app_1       | 2017-06-14 18:57:36.892977 ticker Influx host: 'influxdb'
app_1       | 2017-06-14 18:57:36.892984 ticker Influx port: 8086
app_1       | 2017-06-14 18:57:36.935112 ticker No InfluxDB connection yet. Waiting 5 seconds and retrying.

However, if I open a shell in that specific container using docker exec -ti <container name> /bin/sh, the following works fine:

/ # python3 -u
Python 3.6.1 (default, Jun  8 2017, 21:50:56) 
[GCC 6.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from influxdb import InfluxDBClient
>>> ci = InfluxDBClient(host='influxdb')
>>> ci.get_list_database()
[{'name': '_internal'}]
>>>

I'm sure I'm overlooking something silly, but I'm unable to explain why the app.py won't make a connection. And thus, I'm unable to fix that connection. Any advise here would be greatly appreciated.

My code, for reference, follows below.

app.py:

#!/usr/bin/env python
from influxdb import InfluxDBClient
import datetime
import sys
import time
import os
import requests


def output(msg):
    # Convenience function to always show a correct output
    now = datetime.datetime.now()
    print("%s ticker %s" % (now, msg))


if __name__ == '__main__':
    # Gather our settings
    influx_host = os.getenv('INFLUX_HOST', 'localhost')
    influx_port = os.getenv('INFLUX_PORT', '8086')
    influx_user = os.getenv('INFLUX_USER', 'root')
    influx_pass = os.getenv('INFLUX_PASS', 'root')
    # Create our connections
    # Check to make sure we can create a connection
    got_if_connection = False
    while not got_if_connection:
        output('Trying InfluxDB connection...')
        output("Influx host: %s" % influx_host)
        output("Influx port: %s" % influx_port)
        influx_client = InfluxDBClient(host=influx_host, port=influx_port,
                                       username=influx_user,
                                       password=influx_pass)
        try:
            influx_client.get_list_database()
        except requests.exceptions.ConnectionError:
            output('No InfluxDB connection yet. Waiting 5 seconds and '+
                   'retrying.')
            time.sleep(5)
        else:
            got_if_connection = True

Dockerfile:

FROM python:alpine3.6
MAINTAINER Tim Stoop <[email protected]>

# Copy the script in
COPY app.py /app.py
COPY requirements.txt /requirements.txt

# Install dependencies
RUN pip install -r /requirements.txt


CMD ["python3", "-u", "/app.py"]

docker-compose.yml:

version: '2'
services:
  influxdb:
    image: "influxdb:alpine"
    ports:
      - "8086:8086"
  app:
    build: .
    links:
      - influxdb
    environment:
      - INFLUX_HOST='influxdb'

Please let me know if you need any additional information!