Actually I would run ss over the netstat for such high concurrency connection as netstat hits /proc/net/tcp and it's quite slow. However, you need to have the tcp_diag module loaded otherwise it falls back to /proc/net/tcp.

You may not have read the entire article, but he clearly explains that their tech stack is FreeBSD + Erlang not Linux + Erlang.

There is no /proc/net/tcp on FreeBSD. Hell, there is no /proc unless it is specifically mounted by the administrator, but tools certainly don't use it to get data.

I read it, I just presume people most users are linux based in here.

You might be able to parse /proc/net/tcp yourself faster, especially for just counting by state.

/proc/net/tcp doesn't exist on FreeBSD...

You may have tried but generally add -n to netstat to speed it up by just displaying IPs instead of trying to resolve them. I've never seen a system with so many concurrent connections hands on so there could be some other bottleneck.

netstat -s |grep "connections established" is pretty fast and does the job if you're not filtering for certain ports or IPs. But running plain old netstat on a system with so many connections is a really bad idea. I almost fired myself once over a crufty cron job I left running...