VoIP for buzzer systems: Ensuring a 99.9% availability with a serverless AWS web app
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Project overview
Modern apartment and condo buzzer systems may have made buzzing someone in easy, but they have a distinct flaw. They typically allow connecting only one phone number, and it has to be a local one. So, if a tenant shares a rental with a roommate or two, a single person is on the hook for buzzing in each tenant’s deliveries or friends.
That means the person’s phone could be blowing up with calls from the buzzer system at the most inconvenient of times. And yet, the solution couldn’t be more obvious: tenants simply need a way to connect multiple phone numbers per unit to the buzzer system.
While the solution was simple on the surface, the market was lacking in products that addressed this pain point. Our client, Condo Buzzer, decided to close that gap. Its product would use the VoIP technology to generate a single local phone number and forward calls to up to five connected phone numbers.
Armed with the product vision, market research, and design prototypes, Condo Buzzer turned to us with a request to build a stable, user-friendly, and high-performance VoIP platform.
Services
Challenges
Condo Buzzer needed the product to be highly scalable and available. Additionally, the client wanted to be able to seamlessly switch to an alternative VoIP server if the current one were to fail. That called for a serverless approach to development, as well as the use of AWS to ensure the web application’s availability.
In addition to the product’s main functionality, Condo Buzzer also tasked us with developing the rest of the platform. That included sign-up and sign-in, subscription selection and management, and payment integration.
The whole platform had to be intuitive and easy to use. So, we relied on our user-centered approach to testing and optimization to ensure every workflow was convenient and quick.
Finally, to prevent security risks, we had to ensure that the generated VoIP numbers were communicated safely to each user without causing friction in the user experience. To that end, we opted for automatically sending the VoIP number via email.
Strategic business needs
01 Launch a VoIP product enabling tenants to connect multiple phone numbers to buzzer systems
02 Ensure the platform’s high availability, scalability, and performance
03 Achieve a net promoter score (NPS) above 70 within the first year
04 Secure a user satisfaction rate above 80% within the first year
05 Bring user churn below 15% within the first year
Technical requirements
01 Develop a web application for the VoIP product using a serverless approach
02 Implement user-friendly sign-up, sign-in, and subscription management features
03 Set up local VoIP number generation based on the selected location
04 Implement user-friendly call forwarding and phone number management
05 Integrate the Stripe API for secure payment processing
06 Set up automated emails to communicate the generated VoIP numbers
07 Ensure the app’s seamless deployment to the cloud (AWS)
08 Achieve an application performance index (Apdex) score above 85
09 Ensure application availability above 95%
10 Keep the response time below 0.5s even under peak request volumes
11 Make the app’s interface responsive across screen sizes and devices
12 Conduct user testing to achieve a task success rate of above 85%
We’ll leverage the serverless approach to ensure your application’s consistently high performance and availability under peak request rates.
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Solutions
To ensure the Condo Buzzer application shows high scalability and availability, we opted for combining a serverless architecture with AWS deployment. That, along with our thorough performance testing, allowed the platform to demonstrate a 99.9% availability, <0.3s average response time, and a 91 Apdex score.
We also paid close attention to the user experience throughout the platform. In practice, that meant ensuring interface responsiveness during frontend development and refining user flows based on the feedback received during our testing.
The final product is a cloud-native, serverless web application with a responsive interface and high scalability, performance, and availability. It enables users to:
- Sign up and select their subscription plan
- Generate a local VoIP number and receive it via email
- Set up call forwarding to tenants’ phone numbers
- Manage the connected phone numbers and subscription
- Pay for their subscription via a secure gateway powered by the Stripe API
Sign-up and subscription
New users begin their journey by creating a Condo Buzzer account, selecting their subscription plan, and entering payment details. Subscription plans vary depending on the number of phone numbers that can be connected to the VoIP number. Users can also opt for monthly or annual billing for each plan.
Since these user flows are the first experiences for every new customer, we paid extra attention to their intuitiveness and convenience to ensure the platform makes a good first impression. Thanks to our comprehensive data validation rules during sign-up and UX optimizations based on the testing feedback, the churn rate for this stage of the funnel stayed below 10%.
VoIP number generation and call forwarding
To implement the platform’s core features, we integrated it with a VoIP service, ensuring that our client can easily switch providers if necessary. The service creates a unique number with the local code based on the user’s selected city. Users can then add the tenants’ phone numbers and set up call forwarding for each of them.
In line with our client’s requirements, we made the application server-agnostic. If one VoIP server goes down, the application can easily connect with another one. This approach prevents disruptions and ensures high application availability.
Email notifications
Once the VoIP number is generated, the system automatically sends a confirmation email to the user, along with the number itself. To prevent errors at this step, we added thorough email address verification during sign-up.
We paid close attention to the security of email exchanges with proper communication protocols. The VoIP number isn’t added to the email body; instead, it’s sent in an attached file to further protect it from potential attacks.
Phone number management
At some point, users may need to add new phone numbers to the system, remove the current ones, or switch them up. The phone number management module facilitates each of those tasks by minimizing the number of actions required.
Thanks to our iterative interface improvement, these user flows secured a 93% task success rate during the final round of user testing. The ease of changing the connected phone numbers also contributed to the platform’s overall 88% user satisfaction rate.
Payment processing
We integrated the platform with Stripe to process subscription payments using its API. The integration enables the platform to easily accept a wide range of payment methods, all while ensuring payment data security and regulatory compliance.
We thoroughly tested the API integration to ensure data security between the application and Stripe’s services. We also verified that the API integration can handle peak request rates if necessary.
Subscription management
At some point, Condo Buzzer users may need to upgrade, downgrade, or cancel their subscription. To that end, we implemented an intuitive subscription management module and thoroughly tested its usability.
On top of ensuring intuitive UX, we also verified that the subscription changes are properly communicated to the payment processing gateway. That mitigated the risk of errors in subscription fee processing after the user changes or cancels their plan.
Tech stack
Impact
Thanks to our serverless approach, cloud deployment, and focus on the user experience, Condo Buzzer received a product that secured:
We’ll identify potential security risks in your product’s business logic and mitigate them with a combination of encryption, access controls, and secure communications.
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Darly Solutions' work so far inspires confidence, as they're skilled and trustworthy. The health platform is incredibly happy with their work. The team at Darly is communicative, responsive, and responsible. I’d recommend them to people looking to do more than build a simple little software.
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