Create a Docker image

[bachya]

This PR is a part of https://github.com/jamiebegin/metrics2mqtt/issues/2 and adds a docker folder that contains everything needed to build a Docker image of metrics2mqtt. It uses environment variables to define configuration parameters:

• COMMAND_OPTIONS_STRING: a string of options to send to the metrics2mqtt command (e.g., --cpu=60)
• MQTT_BROKER: the hostname/IP of the MQTT broker
• MQTT_PASSWORD: the MQTT password
• MQTT_USERNAME: the MQTT username

Raw usage:

$ docker run -it -v /proc:/proc -e MQTT_BROKER=localhost -e MQTT_USERNAME=username -e MQTT_PASSWORD=password123 -e COMMAND_OPTIONS_STRING='--cpu=60 --interval=10 --vm --du="/" -vvvvv' jamiebegin/metrics2mqtt:0.1.14

docker-compose usage:

---
version: "3"

services:

  metrics2mqtt:
    container_name: metrics2mqtt
    environment:
      COMMAND_OPTIONS_STRING: '--cpu=60 --interval=10 --vm --du="/" -vvvvv'
      MQTT_BROKER: localhost
      MQTT_PASSWORD: password123
      MQTT_USERNAME: username
    image: jamiebegin/metrics2mqtt:0.1.14
    restart: unless-stopped
    volumes:
      - /proc:/proc

Notes:

• For MVP, this is a single-architecture image – nothing fancy going on to determine AMD64 vs. ARM, etc. That can be a future PR.
• This assumes the image has been pushed to Docker Hub at jamiebegin/metrics2mqtt and tagged with a version consistent with the PyPI package. Obviously, it can be built off of this repo instead.
• We mount /proc inside the container so that metrics2mqtt looks at the host's metrics, not the container's.
• This PR doesn't modify the README at all; in my experience, we shouldn't give users instructions that point them toward building the image themselves. Rather, after the image is published to Docker Hub, we should create a GitHub action that kicks off Docker Hub builds appropriately (on every push to master, every tagged version, etc.). Just a recommendation; open to whatever you want to do here.
• The Dockerfile pins the current PyPI version number of metrics2mqtt when building. So, each time a new version is released, that version number should be updated there, as well.

[bachya]

~Woops: didn't base this off of the correct branch (which I'm assuming should be develop). Will correct.~ Corrected.

[jamiebegin]

Very cool. Thank you!