Docker Basics

From installation to basic concepts, I recommend the video below.

https://www.youtube.com/watch?v=hWPv9LMlme8 

 

Below is an official tutorial for docker beginners.

This post is a short step-by-step review of it.

https://docker-curriculum.com/#our-first-image

A Docker Tutorial for Beginners

 

First thing first: what is Dockerfile?

It's a simple text file that Docker clients calls when creating an image, or, a way to automate the image creation process.

In the tutorial, there's already a docker file in flask-app. Code and its meaning are as below.

# specify base image
FROM python:3.8

# set the working directory
WORKDIR /usr/src/app

# copy all files in this folder (host) to workdir (container) 
COPY . .

# install dependencies
RUN pip install --no-cache-dir -r requirements.txt

# specify the port number that should be exposed (for flask app)
EXPOSE 5000

# command to start running the application
CMD ["python", "./app.py"]

 

The following command runs docker container with port setting.

# run container while connecting port 8888 (host) and 5000 (contianer)
$ docker run -p 8888:5000 yourusername/catnip

 

Open a browser and head to {http://localhost:8888/}.

Seems like it works like a charm!

 

What do we do with multi-container case?

One thing for sure, we can manually run all the necessary containers and connect them with network setting.

The other option is using "Docker Compose".

Docker Compose is for running multi-contiainer Docker apps and provides a config file docker-compose.yml.

 

The tutorial provides a sample docker-compose.yml as below.

It is pretty awesome that a few lines of file can run multi-container docker apps so easily.

version: "3"
services:
  es:
    image: docker.elastic.co/elasticsearch/elasticsearch:6.3.2
    container_name: es
    environment:
      - discovery.type=single-node
    ports:
      - 9200:9200
    volumes:
      - esdata1:/usr/share/elasticsearch/data
  web:
    image: prakhar1989/foodtrucks-web
    command: python3 app.py
    depends_on:
      - es
    ports:
      - 5000:5000
    volumes:
      - ./flask-app:/opt/flask-app
volumes:
    esdata1:
      driver: local