I am trying to establish bandwidth needs for a set of webapps in the company. I am using SNMP to monitor the bandwidth on the eth1 interface, however I am trying to establish what is going over the pipe as far as all the intertwined webapps go.

We have several webapps all hosted on the same tomcat instance, although they are designed so that the different webapps can be hosted on different machines, and as such talk to each other through HTTP.

If webapp A talks to webapp B on the same hosted tomcat instance via HTTP calls, will these values show on the network bandwidth charts, or does linux (CentOS 6.5) or tomcat (7.0) know they are hosted on the same machine and then route them accordingly (through lo1/loopback/localhost or other means).

Many thanks.

  • My guess is that as the packet goes down from layer 5 to layer 4, it will see it is the detestation address, and so the packet will go up again to the application layer. as for which interface will handle the packet, that depend on to which address the URL will resolve to (the public/external address or the internal/lo). – Rabin Aug 26 '14 at 13:54
  • Fire up tcpdump and look. – Zoredache Aug 26 '14 at 14:22
  • Thanks @Rabin, I assumed the same but wondered if anyone had anything concrete. The URL is localhost for now so assumed it was all through loopback but was hoping someone might "know" categorically. – Mitch Kent Aug 27 '14 at 8:36
  • One way you can measure it is by adding a iptable rule to count the packets for each interface. – Rabin Aug 27 '14 at 20:25
  • Thanks Rabin and @Zoredache - in the end we used tcpdump - the difference in ethernet was a symptom we were searching for and tcpdump ended up showing my colleague what they needed so I think from my perspective this is dealt with, although the actual answer to the SF question itself wasn't presented. Can I close my own question as no longer being needed? Or will it just wither away without any answers? – Mitch Kent Aug 28 '14 at 7:57

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