There&#x27;s some notes about how Whatsapp achieved that here [1], they attribute their capacity in part to Erlang&#x27;s concurrency and in part to cloud hosting with SoftLayer.  Amazon is the  origin of SoftLayer&#x27;s cloud services and single biggest reason one engineer can manage arbitrary numbers of servers&#x2F;users:<p><pre><code>    The popularization of the term can be traced to 2006 when 
    Amazon.com introduced its Elastic Compute Cloud. [2]
</code></pre>
[1] <a href="http:&#x2F;&#x2F;research.dyn.com&#x2F;2014&#x2F;03&#x2F;global-consumerwhatsapp&#x2F;" rel="nofollow">http:&#x2F;&#x2F;research.dyn.com&#x2F;2014&#x2F;03&#x2F;global-consumerwhatsapp&#x2F;</a><p>[2] <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Cloud_computing#History_of_cloud_computing" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Cloud_computing#History_of_clo...</a>