Using top tcp

The top tcp gadget is used to visualize active TCP connections.

On Kubernetes

First, we need to create one pod for us to play with:

$ kubectl run test-pod --image busybox:latest sleep inf

You can now use the gadget, but output will be empty:

$ kubectl gadget top tcp
NODE            NAMESPACE       POD             CONTAINER       PID     COMM    IP REMOTE                LOCAL                 SENT    RECV

Indeed, it is waiting for TCP connection to occur. So, open another terminal and keep and eye on the first one, exec the container and use wget:

$ kubectl exec -ti test-pod -- wget kinvolk.io

On the first terminal, you should see:

NODE            NAMESPACE       POD             CONTAINER       PID     COMM    IP REMOTE                LOCAL                 SENT    RECV
minikube        default         test-pod        test-pod        134110  wget    4  188.114.96.3:443      172.17.0.2:38190      0       2
minikube        default         test-pod        test-pod        134110  wget    4  188.114.96.3:80       172.17.0.2:33286      0       1

This line corresponds to the TCP connection initiated by wget.

Clean everything

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

$ kubectl delete pod test-pod
pod "test-pod" deleted

With local-gadget

Start a container that runs nginx and access it locally:

$ docker run --rm --name test-top-tcp nginx /bin/sh -c 'nginx; while true; do curl localhost; sleep 1; done'

Start the gadget, it’ll show the different connections created the localhost:

$ sudo local-gadget top tcp -c test-top-tcp
CONTAINER                                              PID         COMM             IP LOCAL                 REMOTE                SENT                 RECV
test-top-tcp                                           564780      nginx            4  127.0.0.1:80          127.0.0.1:35904       238B                 73B
test-top-tcp                                           564813      curl             4  127.0.0.1:35904       127.0.0.1:80          73B                  853B