Using trace sni

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

On Kubernetes

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

$ kubectl gadget trace sni
NODE               NAMESPACE          POD                PID        TID       COMM      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
root@ubuntu:/# apt update && apt install -y wget && wget wikimedia.org
(...)
HTTP request sent, awaiting response... 301 Moved Permanently
Location: https://www.wikimedia.org/ [following]
(...)
root@ubuntu:/# 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:

NODE               NAMESPACE          POD                PID        TID       COMM      NAME
minikube           default            ubuntu             3917791    3917791   wget      www.github.com
minikube           default            ubuntu             3917791    3917791   wget      github.com
minikube           default            ubuntu             3917812    3917812   wget      wikimedia.org
minikube           default            ubuntu             3917812    3917812   wget      www.wikimedia.org

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

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

With local-gadget

Run the gadget in a terminal

$ sudo local-gadget trace sni -r docker -c test-trace-sni
CONTAINER                              PID        TID        COMM             NAME

Run a containers that establishs a TLS connection with a remote endpoint:

$ docker run -it --rm --name test-trace-sni busybox /bin/sh -c "wget https://example.com"
Connecting to example.com (93.184.216.34:443)
wget: note: TLS certificate validation not implemented
saving to 'index.html'
index.html           100% |*******************************************************************************************************************************************************************|  1256  0:00:00 ETA
'index.html' saved

The gadget will show that Server Name Indication used by the request.

$ sudo local-gadget trace sni -r docker -c test-trace-sni
CONTAINER                              PID        TID        COMM             NAME
test-trace-sni                         3944366    3944366    wget             example.com