Receive UDP Packets on Google Compute Engine

Question

my task is to receive UDP packets on an Google Compute Engine. Given is the port, which is 300 and I already have a simple Java program which can handle these UDP packets.

My problem now. Get the UDP packets to my Java program.

For that I don't know how to do this. What I have tried so far ist to let the Java program direct listen to the port, which didn't work. I suspect the traffic from outside the GCE must be routed to the inside?

Answer 1

First make sure you've added a firewall rule on your GCE VM instance's network which allows incoming traffic for UDP protocol on port 300. You can do this by going to the Developers Console, select your project, then Compute-> Compute Engine-> Networks, click on the right network and verify firewall rules (and tags as well if you used them). If the rule is not added, then add a rule for the traffic.

"gcloud" is a command-line tool which you can use it to list and verify your firewall rules as well [1]:
$ gcloud compute firewall-rules list

If the firewall rules are good, then use a simple troubleshooting tool like netcat to test if traffic is being forwarded to your VM instance.

1. Listing Google Compute Engine firewall rules

Answer 2

I recommend not using Java to process UDP. I experienced inexplicable short periods where all UDP traffic arriving was being lost. This was caused by garbage collection.

The architecture that works for me is to use a GCE VM with a C++ app receiving UDP data, then using libCURL, convert the data to HTTP and dispatch it to Google App Engine for processing. To make the UDP receiver scalable and tolerant, use network balancing and multiple VMs listening for UDP.