OCI Daily: From Mock API Server to Mandelbrot Sets over the Load Balancer, CloudFlare, Let's Encrypt and Beyond...

Hello everyone! It's been a while since I last shared my thoughts, but I've been deep in the trenches of a fascinating new stuff. You know how things are, it started with a simple need for a mock API server and led me through setting up load balancers, domain management, and fun with Mandelbrot sets. Let me take you through it. This can be used as a blueprint for deploying your web workload securely on modern cloud environments.

Setting the Stage with a Python Flask App

Normally a quick dirty python http.server is enough for testing accessibility but this one time we needed a bit more than that. It all began with a customer request that they needed to setup a mock API server. A Python Flask app seemed to be a suitable option for that time: I've never used it before. I must admit curiosity and growing pythonic love inside me made me do this choice. This initial step, though seemingly straightforward, laid the groundwork for the exciting challenges that followed. There are lots of tutorials to get you started, just start with this link.

Load Balancers, Domains, and the Birth of CodeHarmony.Net

I was just playing around with my new Flask app, discovering blueprints , jinja templates etc., you know usual things. Then another customer came with a fair request:

I want to use my load balancer with multiple backends accessible via different domains and subdomains.

Which is possible with Virtual Hostnames . Start with adding your hostnames (actual DNS A Records).

Then you need to decide if

you want to use one listener for each backendset (which implies each listener will be using a different port) e.g. codeharmony.net:443, files.codeharmony.net:444, etc... Straightforward if you are okay with different ports. Just select the hostname(s) during listener creation.
you want to use one listener for all backendsets (which implies you should be able to distinguish by the requested URI). This one a little tricky and requires proper planning. You need to combine hostnames and path route sets. Here is the official documentation

For testing this in my tenancy I needed a domain, well, mmm... Maybe not, I could just edit my host file but to be honest I wanted to also test deploying my Flask app and see it live instead of scraping it. This prompted the creation of CodeHarmony.Net . I followed the hype, and the name born out of collaboration with ChatGPT. With a smooth purchase from Namecheap , CodeHarmony became the hub for my tech experiments

Navigating the Cloud with Cloudflare and SSL/TLS Encryption

You know, these are the basic steps to ensure a secure and efficient web deployment.

I created a free Cloudflare account, with basic protection to proxy connections to my loadbalancer as I don't want them to be exposed to all internet directly.
Then I updated nameservers on my domain name provider (Namecheap) with the ones CloudFlare provided.
Then created domain and subdomains (A Records) using my Load Balancer Public IP
Then proxied the connection to load balancer. I implemented full strict SSL/TLS encryption, terminating at the load balancer (which means private subnet traffic is not encrypted)
On load balancer end, configured listeners for both HTTP and HTTPS. I mentioned a little about routing above.
To make sure all traffic is supported and encrypted I also created an HTTP listener and redirected all HTTP to HTTPS using URL Redirect Rules
Cloudflare brings it own TLS certificates which is very cool. For my loadbalancer HTTPS Listener I used a free Let's Encrypt certificate.
I restricted access to my loadbalancer to CloudFlare IP addresses (I am not sure if I whitelisted all of them though...). One cool thing I noticed while investigating loadbalancer access logs, CloudFlare sends end client IP address in forwardedForAddr field. Here is a simplified access log:

Flask Web App Deployed on Container Instances as Backend

For those who share my passion for coding adventures, all code is available on my Github repo . Dive in, explore, and feel free to contribute. Dockerfile is also included as it is packaged as a container. You will also find a build-and-deploy.sh file which is building the container image, pushing it to a private OCI registry then creating container instance. You need to prepare .env file which is not included in the repo, the file should contain following values: Once set you should be able to build and deploy your application. Just notice that I am using London region, if you use another remember to change values including OCI Registry.

It was super fun to design, code, build and deploy everything with the best practices applied. It felt good when put myself to test and find out that I can still code Full Stack with a basic Python/Flask backend with Bootstrap and JQuery for the frontend. I was a bit rusty in the begining but progressed very fast. Admittedly, React or Vue might have been the trendy choices, but the experience proved invaluable, reigniting my confidence in full-stack development.

You will find many scripts converted into tools in these pages: manipulating PDF files, playing around with images. Captivating world of Mandelbrot sets which is a beauty of drawing, painting, and exploring color palettes became my newfound fascination, leading to the discovery of hidden gems waiting to be unveiled.