Using trace sni

The trace sni gadget is used to trace the Server Name Indication (SNI) requests sent as part of TLS handshakes.

How to use it?

The SNI tracer will show which pods are making which SNI requests. To start it, we can run:

$ kubectl gadget trace sni
POD                            NAME

To generate some output for this example, let’s create a demo pod in another terminal:

$ kubectl run -it ubuntu --image ubuntu:latest -- /bin/bash
[email protected]:/# apt update && apt install -y wget && wget wikimedia.org
(...)
HTTP request sent, awaiting response... 301 Moved Permanently
Location: https://www.wikimedia.org/ [following]
(...)
[email protected]:/# wget www.github.com
(...)
HTTP request sent, awaiting response... 301 Moved Permanently
Location: https://github.com/ [following]
(...)

Go back to the first terminal and see:

POD                            NAME
ubuntu                         wikimedia.org
ubuntu                         www.wikimedia.org
ubuntu                         www.github.com
ubuntu                         github.com

We can see that each time our wget client connected to a different server, our tracer caught the Server Name Indication requested.

Use JSON output

This gadget supports JSON output, for this simply use -o json, and trigger the output as before:

$ kubectl gadget trace sni -o json
{"type":"debug","message":"tracer attached","node":"minikube","namespace":"default","pod":"ubuntu"}
{"type":"normal","node":"minikube","namespace":"default","pod":"ubuntu","name":"wikimedia.org"}
{"type":"normal","node":"minikube","namespace":"default","pod":"ubuntu","name":"www.wikimedia.org"}

Clean everything

Congratulations! You reached the end of this guide! You can now delete the pod you created:

$ kubectl delete pod ubuntu
pod "ubuntu" deleted