How to Containerize Your App with Docker

Wrangling production, staging, and development environments can prove a herculean task, and can be wrought with potential errors and inconsistencies. This is where Docker enters the frame, simplifying the process by creating an isolated environment or 'container' for your app.
In this guide, you will learn how to containerize your applications using Docker, a scalable and highly reliable option favoured by developers world over.

Why Choose Docker?

Docker is an open-source platform that harnesses OS-level virtualization to distribute software in packages called containers. With Docker, you package your application with all the dependencies it needs to run, in an isolated container. This ensures that the application will run irrespective of any distinctive settings the machine may have.
But what truly sets Docker apart is its simplicity, fast deployment times, and compatibility with numerous system platforms.

Prerequisites to Containerization with Docker

Before proceeding, there are few requirements to satisfy. You must have Docker installed on your system. Furthermore, you should be familiar with the basics of Docker and understand the purpose and structure of 'Dockerfile'. Lastly, you should have a basic understanding of the application you intend to containerize.

Creating a Dockerfile

The first step to containerizing your app is creating a Dockerfile. This is a simple text file that tells Docker what to do. This file includes directives to instruct Docker regarding which base image to use, which ports to open, and which files or directories to add the container.
Here's a basic outline:

#Use an official Python runtime as a parent image

FROM python:2.7-slim

#Set the working directory in the container

WORKDIR /app

#Copy the current directory contents into the container

ADD . /app

#Install any required dependencies

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

#Make port 80 available to the world outside this container

EXPOSE 80

#Define environment variable

ENV NAME World

#Run app.py when the container launches

CMD ["python", "app.py"]

Building Your Docker Image

Once your Dockerfile is ready, the next step is to build the Docker image. This is accomplished using the 'docker build' command. Tag your image using the '-t' option to make it easier to find later.

docker build -t myapp:latest .

Running Your Docker Image

Finally, you can run your Docker image using the 'docker run' command. This will run your app in a new container.

docker run -p 4000:80 myapp

Your app is now contained in a Docker container and accessible at localhost:4000.

In conclusion, Docker simplifies the software deployment process by creating isolated, consistent environments for your app. It is a developer's loyal aide and distributing an app has never been more reliable and easy.