Docker

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Docker

Docker is the number 1 development tool. It helps developers build applications without configuration or environment setup.

It removes the “well, it works on my machine” problem many face when sharing code/dependencies.

Containers

Docker uses containers. A container is a process running on a computer that is separate or isolated from all other processes.

They leverage software like kernel namespaces and cgroups available within the Linux operating system.

Images

Containers run on filesystems provided by an image. These are configurations of everything needed to run an application including:

and more.

Multiple containers can be “spun up” from a single image.

Installation

Docker is made up of multiple components. The easiest way to install Docker is to run Docker Desktop.

This is a “batteries included” GUI program that enables users to run containers.

Dockerfile

Everything in Docker runs off a single Dockerfile. This is the default filename and does not have an extension. Using this name allows you to run the docker build command without having to specify additional command flags.

This file contains instructions on how to build images.

The basic format is:

# Comment
INSTRUCTION arguments

Workflow

Below is a small Flask code snippet:

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

To run this code, you would need to:

That’s a lot of work.

This sample Dockerfile creates a container image with everything needed to run the app.

# syntax=docker/dockerfile:1
FROM ubuntu:22.04

# install app dependencies
RUN apt-get update && apt-get install -y python3 python3-pip
RUN pip install flask==3.0.*

# install app
COPY hello.py /

# final configuration
ENV FLASK_APP=hello
EXPOSE 8000
CMD ["flask", "run", "--host", "0.0.0.0", "--port", "8000"]

To build the container, you would run the following command:

docker build -t test:latest .

And to run the container:

docker run -p 127.0.0.1:8000:8000 test:latest

This maps the container’s port 8000 to http://localhost:8000 on the server.

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