I have automated the deployment of my application via fabric and have a new step that I need to add where I take my application out of rotation in the load balancer then, watch inbound connections from the balancer until they go to 0. Problem is, I am not sure how to get the count of inbound connections.
I can use tcpdump to watch my port POSTs. However, this is kind of hard to use in fabric. What I would like is to just run a loop with a timer that keeps getting the number of active inbound connections and exits on 0. Has anybody done anything like this? Or maybe someone would know how I might be able to achieve this from the shell and I can put it in fabric?
netstat is one of the simplest ways to get this information, however, as you have noted, simply using grep to parse the output of netstat yields sub-optimal results, because it will match both incoming and outgoing connections (at least without a sufficiently complex search expression, or preprocessing with cut or the like). I would suggest this route, instead:
netstat -ap | awk '$1 == "tcp" && $4 ~ /:(80|443)$/' | wc -l
This will count connections that are TCP-based, and the local end is connected to either port 80 or 443, which would correspond with incoming connections. Replace $4 with $5 in that to catch outgoing connections instead.