We are currently running the infrastructure on AWS (Amazon Web Services), its currently running on single Application server with below hardware configuration;

Instance Type      : C3xLarge
CPU cores          : 4
Memory (RAM)       : 7.5GB
SSD HDD            : 50GB
Capacity           : 1680 req/s
Transfer speed     : 859.54 KB/s

Mysql Version      : 5.6.28
Ejabberd Version   : 15.07 (10000 connections per server)
Ruby Version       : 2.2.3p173
GEM version        : 2.4.5.1

Gem list;

*** LOCAL GEMS ***

backports (3.6.7)
bigdecimal (1.2.6)
bundle (0.0.1)
bundler (1.11.2)
capistrano (3.4.0)
capistrano-bundler (1.1.4)
capistrano-ext (1.2.1)
capistrano-log_with_awesome (0.0.2)
capistrano-passenger (0.2.0)
capistrano-rails (1.1.6)
capistrano-rbenv (2.0.4)
capistrano-stats (1.1.1)
god (0.13.7)
highline (1.7.8)
i18n (0.7.0)
io-console (0.4.3)
json (1.8.1)
minitest (5.4.3)
net-scp (1.2.1)
net-ssh (3.0.2)
passenger (5.0.23)
power_assert (0.2.2)
psych (2.0.8)
rack (1.6.4)
rake (10.4.2)
rdoc (4.2.0)
specific_install (0.3.1)
sshkit (1.8.1)
test-unit (3.0.8)

LoadBalancer - C3xLarge (For Network Bandwidth)
MySQL        - C3xLarge (For Memory)
Application Server - M4xlarge