Currency Rates viewer

Web application for displaying currency exchange rates present and past.

It uses the "Free Currency Exchange Rates API" https://github.com/fawazahmed0/currency-api

Webframework

Uses the python web framework Flask with its development webserver (TODO move to nginx), to provide a frontend with html form input processing, redirections, html page rendering and to call the currency API and processes the data.

Jinja2-templating engine is used to generate the html website code.

The flask extentension WTForms provides the frontend html form in which the user can choose the currency and date they care about being rendered into a chart.

The chart.js JS library is used to render an interactive bar-chart displaying the currency exchange rate data.

Containerization

The web application is containerized on top a python:3.10.5-apline image layer. Here a python virtualenvironment is created containing all the necessary flask modules and prepared to launch the application inside it.

The container is managed via docker-compose, by providing a service with abuildpath of the Dockerfile and the port to be attached to the host machine.

Ansible: provisioning

Example preperation

• hostnamectl set-hostname linode
• timedatectl set-timezone Europe/Berlin
• localectl set-locale C.UTF-8
• useradd ansible --create-home --shell /bin/bash
• sudoers entry for ansible (easy become)

Installation

docker compose: run docker compose up or docker-compose up inside app/docker-compose.yml. This will by default make the web service available on Port 5000.

Ansible: use Ansible playbook to install the service on a given server (written for Ubuntu 22.04 LTS) with:

ansible-playbook -i hosts.ini curr-rates-playbook.yml -k

The playbook needs needs to run with root priviledges.

example api call:

To query the exchange rate of the Euro on the 21. of october 2022: https://cdn.jsdelivr.net/gh/fawazahmed0/currency-api@1/2022-10-21/currencies/eur.json

TODO

Error Handling

• fallback url
• Input validation: force Date range; missing dates
• HTTPError handling with error pages redirection

Performance

• Cache API calls (mnemonize with currency/date as keys)

Security

• .env for Environment Variables (e.g. SECRET_KEY)
• webserver: nginx
• https with Let's encrypt

Usability

• real-time Currency filtering
• Frontend: prettify with css/bootstrap