đŹ From Rejection to Revolution: The Engineering Brilliance Behind WhatsApp
đ± The Incredible Engineering Story Behind WhatsApp
Today I stumbled upon the incredible story behind WhatsAppâone of the most successful instant messaging platforms in historyâand found it absolutely captivating.
Jan Koum, a former Yahoo engineer, was once rejected by Facebook. Ironically, just a few years later, Facebook acquired WhatsApp for a staggering $19 billion. Alongside co-founder Brian Acton, Koum built a product that transformed global communicationâand did so with remarkable engineering discipline.
Here are some key takeaways from WhatsAppâs technical journey that every developer and architect can learn from:
đ§ 1. Single Responsibility Principle
WhatsApp was laser-focused on one goal: replacing expensive SMS.
No ads, no social feed, no distractions. This clarity of purpose helped it scale rapidly without compromising user experience.
âïž 2. Smart Technology Choices
WhatsAppâs backend was built using Erlang, a language designed for massive concurrency.
Unlike Java or C++, Erlangâs lightweight processes are managed by its own virtual machine (BEAM), allowing millions of simultaneous connections with minimal overhead.
This made context switching extremely efficient, enabling WhatsApp to handle real-time messaging at scale.
𧱠3. Building on Open Source
Rather than reinventing the wheel, WhatsApp was built on Ejabberd, an open-source XMPP server written in Erlang.
This decision accelerated development and allowed the team to focus on performance and reliability.
đ 4. Scaling with Simplicity
WhatsApp initially leaned into vertical scalingâmaximizing the power of individual serversâbefore layering in horizontal scaling as needed.
This hybrid approach kept infrastructure costs and complexity low while supporting exponential growth.
đ 5. Seamless Deployment
Running on FreeBSD, WhatsApp leveraged Erlangâs hot code swapping to deploy updates with zero downtime.
While their CI/CD pipeline wasnât publicly detailed, their ability to push changes without interrupting service was a testament to thoughtful engineering.
đ„ 6. Small Team, Big Impact
At the time of acquisition, WhatsApp had just 32 engineers supporting over 450 million users.
This wasnât just leanâit was legendary. A small, focused team with clear goals outperformed giants.
đ Final Thought
WhatsAppâs story is more than a tale of startup successâitâs a masterclass in engineering focus, smart choices, and purposeful simplicity.
Whether you’re building your own product or scaling an existing one, thereâs a lot to learn from how WhatsApp did it.
đ Read more: WhatsApp Engineering Journey
