"What has hundreds of nodes, thousands of cores, hundreds of terabytes of RAM, and hopes to serve the billions of smartphones that will soon be a reality around the globe? The Erlang/FreeBSD-based server infrastructure at WhatsApp. We've faced many challenges in meeting the ever-growing demand for our messaging services, but as we continue to push the envelope on size (>8000 cores) and speed (>70M Erlang messages per second) of our serving system."

Stats

• 465M monthly users.
• 19B messages in & 40B out per day
• 600M pics, 200M voice, 100M videos
• 147M peak concurrent connections - phones connected to the systems
• 230K peak logins/sec - phones connecting and disconnecting
• 342K peak msgs in/sec, 712K out
• ~10 team member works on Erlang and they handle both development and ops.
• Holidays highest usage for multimedia.
• 146Gb/s out (Christmas Eve), quite a bit of bandwidth going out to phones
• 360M videos downloaded (Christmas Even)
• 2B pics downloaded (46k/s) (New Years Eve)
• 1 pic downloaded 32M times (New Years Eve)

Read the rest of Todd Hoff's detailed blog post on High Scalability.