Calculator

This is a simple flask web app which will run a calculator program in the browser.

Installing on an AWS EC2 instance

Background

All of these commands should be run from a session on the AWS EC2 instance you wish to install the calculator webapp on.

Flask is a minimalistic Python library for creating web server applications. For this assignment all we have to do is install flask and run the program here.

This guide roughly follows the basic Flask install steps

Dependencies

These are the dependencies required for this project. Installation steps are below.

• a package manager - apt or yum (or brew for that matter)
• git
• python3
• pip
• flask

Installation

Run sudo apt update or sudo yum update to update your package manager. We will use apt in the guide code here but you can replace apt with yum and everything should work.

Installing pip

pip is a Python package manager - it is the recommeneded tool for installing Python packages. We will install pip and use it to install the flask library/package.

Confirm you have python3

Run which python3 and python3 --version to confirm Python 3 is installed.

Note: Python 2 may be installed as python -- python --version may show python version 2. If this is the case be sure to use the python3 command. Many linux systems are set up this way for backwards compatibility with Python 2 programs. Using python 2 is not recommended.

Now run which pip to confirm that pip is not installed.

For the following steps we will use the apt package manager. If you are on a Linux system and apt is not installed but yum is, use yum.

sudo apt update
sudo apt install pip

Now type pip --version to confirm pip was successfully installed.

Installing git

If git is not installed (run git --version to check), install git: sudo apt install git.

Cloning this repo

Run git clone https://github.com/codeplatoon-devops/calculator-webapp.git -- this will "clone" this git repo and make a copy of it on your machine.

Navigate to project directory

cd calculator-webapp

Create & activate Python virtual environment

A python virtual environment is a fancy term for a directory holding the python packages and correct version of the python language that our project uses.

We will learn more about this later, for today we will just follow these steps to get our flask server running.

Run the following commands in the project directory:

python3 -m venv .venv
source .venv/bin/activate

Your python virtual environment is now created and activated. Now, anything you install with pip is installed within this virtual environment. You are not using multiple python virtual environments so don't have to worry about de-activating your environment; it is very lightweight and will not affect anything.

If you are curious, running deactivate will deactivate the virtual environment and source .venv/bin/activate will re-activate it again.

Installing flask

With the virtual environment activated run pip install flask to install flask. If there is a requirements.txt file you could also run pip install -r requirements.txt to install all the python dependencies (such as flask) in the requirements.txt file.

Running the webserver

Run: python3 calc.py

The webserver should be run on port 8080.