Assumptions

  • You have a CF deployed
  • You have one proxy app pushed and called appA
  • You have one route mapped to appA called APP_A_ROUTE
  • You have completed the previous stories in this track

Recorded values from previous stories

APP_A_ROUTE=<value>
APP_A_GUID=<value>
DIEGO_CELL_IP=<value>
CONTAINER_APP_PORT=<value>
DIEGO_CELL_APP_PORT=<value>
CONTAINER_ENVOY_PORT=<value>
DIEGO_CELL_ENVOY_PORT=<value>
OVERLAY_IP=<value>

What

Netstat is a tool that can show information about network connections, routing tables, and network interface statistics. In the previous story we saw that the GoRouter sent traffic for APP_A_ROUTE to DIEGO_CELL_IP:DIEGO_CELL_ENVOY_PORT. Let’s use netstat to see what is listening at on the Diego Cell and specifically at DIEGO_CELL_IP:DIEGO_CELL_ENVOY_PORT.

How

📝 Look at open ports on a Diego Cell

  1. Ssh onto the Diego Cell where appA is deployed and become root.
  2. Use netstat to look at open ports 
    netstat -ntulp
# -n  <---- show raw ip addresses and socket numbers
# -t  <---- show tcp sockets
# -u  <---- show udp sockets
# -l  <---- display listening sockets
# -p  <---- display PID/program name for sockets

    You should recognize the program names in the far right column. Most of them are the long running cf component processes.

  3. Find the local address for the Route Emitter. What port is it running on? Does that match what is in the spec file?

  4. Search for DIEGO_CELL_ENVOY_PORT in the output. Can you find it?

Expected Result

You won’t see the DIEGO_CELL_ENVOY_PORT anywhere in the netstat output because nothing is actually running there. But if there’s nothing running there, how does the traffic reach the app? Would you believe that iptables are involved? Check out the next story to learn more :)