I use the latest Puma v1.4.0 from rubygems.
Make sure you have nginx installed with these options:
>/opt/nginx/sbin/nginx -V
nginx version: nginx/1.0.15
built by gcc 4.6.1 (Ubuntu/Linaro 4.6.1-9ubuntu3)
TLS SNI support enabled
configure arguments: --prefix=/opt/nginx --with-http_ssl_module --with-http_gzip_static_module --with-cc-opt=-Wno-error --add-module=/usr/local/rvm/gems/ruby-1.9.3-p0/gems/passenger-3.0.12/ext/nginx --with-http_ssl_module --with-pcre=/tmp/pcre/pcre-8.30
We installed nginx using passenger as you can see above, as we run currently most apps with it, but that is of course not required for puma to run.