Introduction to Docker

This repo deals with the building of a flask app then containerise it using docker and deploying the resulting docker image onto heroku. The following instructions assume that you have already installed docker and heroku-cli if not then follow the instructions in the pre-requisites section for doing so.

Pre-requisites

Docker

Follow the steps 1 and 2 and then check your installation by doing step 3 in the following Link.

Heroku-cli

For heroku-cli installation in ubuntu 16+ versions use the following command

sudo snap install --classic heroku

Procedure

STEP 1:

Clone this repo using the following command:

git clone https://github.com/aswarth123/Introduction_to_Docker.git

and then cd to this repo using cd Introduction_to_Docker This repo has the following directory structure:

Introduction_to_Docker
      ---templates
         ---index.html
      ---Dockerfile
      ---LICENSE
      ---README.md
      ---app.py
      ---requirements.txt

STEP 2:

Now we will create the Docker image of the app in the following manner:

docker image build -t intro_to_docker .

The -t flag is used here to give the name of the newly created image. Note: This command may take 10-15 mins to execute depending upon your internet connectivity speed.

After the execution of the above command use

docker image ls

command to list out all the docker images you have and now you will be able to see the intro_to_docker image as well.

STEP 3:

In this step we will be running our docker image using the following command

docker run -p 5000:5000 -d intro_to_docker

Now click on this link to see whether the docker app is running in your local machine and you will be able to see the Hello world to Docker on your screen.

STEP 4:

Now stop the container running at Localhost at port 5000 using the following commands:

docker container stop <container id>
docker system prune

Note: The container id you will get from the output of the previous commands that you executed.

STEP 5:

This step deals with the deployment of your docker container onto heroku.

Login

At first you need to login to heroku using the following command

heroku container:login

This would open the browser and prompt you to log in with your Heroku credentials. If you succeed in logging, you will receive a message “Login Succeeded”.

App creation

For a creating a heroku app use the following command and give it a name.

heroku create <name-for-your-app>

After executing the following command you will get the following link as an output which is a link to your heroku app that you created. https://<name-for-your-app>.herokuapp.com/

Pushing the container to heroku

Use the below command to do so.

heroku container:push web --app <name-for-your-app>

Note: The succesful execution of this command may take some time (~20 mins) depending on your internet connectiviy.

Deploying the app

At this point, the docker container is pushed to Heroku, but not deployed or released. The following command would deploy the container:

heroku container:release web --app <name-for-your-app>

Now, the app is released and is running on Heroku and you can view it on the below link.
https://<name-for-your-app>.herokuapp.com/

Thus, we successfully dockerized and deployed our Python Flask app onto Heroku.