<h2>Introduction</h2>

 Here, I'd like to talk about one of my breakthrough projects.
 First, I'll discuss the main function of the app, then I'll share one of the
 biggest challenges we faced during the project and how I approached solving
 it. I highly recommend reading this article to the end; I’m sure you’ll gain
 valuable insights.


<h2>Project Overview</h2>

 It has happened many times to all of us in our work environment: a decision
 needed to be made, but it required employees’ input.
 How great would it be if employees could share their ideas
 anonymously?
 This way, employees could share their truest thoughts without worrying about
 being judged by others.


 You got the point! Our application was designed to help
 businesses run voting campaigns, allowing employees to share their feedback on
 specific topics. Each employee had their own dashboard in the app, where they
 could see the topic and voting options, with the ability to cast their vote.
 The interesting part was that after casting their vote, they could see the
 real-time results until the voting period ended. Once the voting ended,
 everyone was notified about the most selected option, allowing them to be
 aware of the decision that would be made.


<h2>Problem Statement</h2>

 One day, my manager called me and said that most of our business partners had
 requested a notification system for our app to:

<ul>
 <li>Notify employees when a new vote starts.</li>
 <li>
 Send reminders as the voting deadline approaches for those who haven’t
 voted yet.
 </li>
 <li>
 Inform everyone about the most selected option once the voting
 ends.
 </li>
</ul>

 Then, my manager added,
 "This feature could be a game-changer for our app. I'm confident that it
 will make our business partners very happy and give them more assurance that
 employees won’t forget to cast their votes or miss a voting
 opportunity."



 Since most of our business partners were active Slack users, after a long
 discussion and some back-and-forth, we finally decided to build a
 comprehensive notification system that could send messages via both
 email and Slack.


<h2>Research and Planning</h2>

 I immediately started my own research so I could provide my manager with a
 clear report covering the
 feasibility, challenges, timeline, and tools required for
 developing this feature. To make a long story short, we decided to use
 Sendinblue (Brevo) as our SMTP server. I
 also realized that Slack provides a great API, allowing us to
 access the Slack workspaces of our business partners using the
 OAuth2 methodology.


<h2>Development Phases</h2>

 I planned to break the development of this feature into
 three phases:

<h3>Phase 1:</h3>

 Preparing logical scripts to ensur that notifications are sent at a precise
 time to the correct user.

<h3>Phase 2:</h3>

 Building scripts/functions to send the appropriate reminders with predefined
 dynamic variables via both Slack and email.

<h3>Phase 3:</h3>

 Building the OAuth system, allowing businesses to integrate
 their Slack workspace with our application and associate a
 specific Slack channel to send our notifications in that
 channel.


<h2>Challenge We Faced</h2>

 After completing these three phases, everything was
 functional and working great until we reached a stage where
 the increasing number of
 business partners and employees caused
 significant CPU spikes. This led to some
 breaks in the functionality of our application.



 My manager promptly called me and asked me to
 investigate why the app was not working as expected. After a
 thorough investigation, I realized that our application was
 not capable enough to handle a large number of
 concurrent requests efficiently.


<h2>Finding a Solution</h2>

 I knew that my manager didn’t just want to hear the reasoning behind this
 issue; she wanted a solution. In my report, I suggested
 adding Celery as a task manager to our app. This way:

<ol>
 <li>
 Tasks could be queued and completed by another worker, significantly
 improving the app's functionality.
 </li>
 <li>
 We could manage scheduling tasks programmatically rather than relying on
 the server's cron jobs.
 This would give us
 more control over every aspect of the system.
 </li>
</ol>

 Implementing Celery worked perfectly for our app for the
 first two years. However, once the
 number of users exceeded our expectations, even
 Celery alone was no longer efficient, and our
 server again experienced CPU spikes.


<h2>Batching System Implementation</h2>

 This time, after talking with my manager, I proposed
 vertical or horizontal scaling of our servers as the
 fastest way to overcome the issue. However, like most
 startups that are cautious about spending, my manager refused
 this approach and wanted me to find another solution.


 To explore alternative solutions, I
 reviewed the scripts once more, conducted
 additional research, and eventually came up with an idea:
 implementing a batching system.

<ul>
 <li>Break them into smaller groups.</li>
 <li>Send notifications to one batch at a time.</li>
 <li>Introduce a short pause.</li>
 <li>Proceed to the next batch.</li>
</ul>

 This approach significantly reduced CPU load while
 maintaining efficiency. After implementing this solution,
 the application remained stable for a long time, and it’s still working
 effectively today.


<h2>Next Step?</h2>

 So, what are your thoughts? If we again face a break in our
 app, would you suggest:

<ul>
 <li>Vertical scaling?</li>
 <li>Horizontal scaling?</li>
 <li>Or do you have a more cost-effective approach?</li>
</ul>
I’d love to hear your insights!

The application was designed to enable businesses to run voting campaigns while allowing employees to share their feedback anonymously. As part of this project, I led the development of a scalable notification system using Sendinblue (Brevo), the Slack API, and OAuth2 to automate reminders and ensure no one forgets to cast their vote. I further implemented Celery as a task manager in combination with a batching system to optimize performance while solving key scalability challenges.

A scalable Notification System for a Voting Application: Email & Slack Integration