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In Apache prefork server running PHP application on Linux, each HTTP request might fetch some data from other server, for instance Memcached. Let's say we want to find out top 10 HTTP requests (ex. GET /blabla) that take the most bandwidth to Memcached. Is there any way to monitor how much outgoing bandwidth was taken per HTTP request without modifying the PHP application?

My approach was using tcpdump and netstat or /proc/net/tcp. With the below command, it'd collect incoming HTTP traffic and outgoing one. But I can't tell which particular HTTP request makes which Memcached connections easily. While it's Apache prefork, PID for every HTTP request can be logged, though tcpdump doesn't know which process made those packets.

tcpdump -i any src port 80 or port 11211 -w tcpdump.log

With netstat, often I find PID information is missing in its output.

netstat -tpc >netstat.log

To map PID to connected sockets, I can possibly scan /proc and get process id and local ports. So, I have a pair of PID and a list of local ports that connected to Memcached. By searching those port numbers in tcpdump.log, I get the length of the packets.

I'm not sure if scanning the entire directory every second or even more frequently would be efficient while the Apache spawns 100+ processes in my case. Thought there might be a better way.

  • @Fabian I'm aware of mod_status, but it doesn't capture the number of bytes used between Apache and other servers. Am I missing something? – Nobu Apr 30 '18 at 18:30
  • Browser <- (A) -> Apache <- (B) -> Memcached -- mod_status collects the number of bytes served by Apache which is (A). That's not outgoing network usage I want. – Nobu Apr 30 '18 at 21:14

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