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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
K8S.NODE         K8S.NAMESPACE    K8S.PODNAME      K8S.CONTAINERNAME PID       COMM      IP SRC                   DST                   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 1.1.1.1

On the first terminal, you should see:

K8S.NODE           K8S.NAMESPACE K8S.PODNAMECONTAINER   PID         COMM       IP SRC                        DST                  SENT       RECV
minikube-docker    default       test-pod   test-pod    289548      wget       4  p/default/test-pod:47228   r/1.1.1.1:443        296B       15.49KiB
minikube-docker    default       test-pod   test-pod    289540      wget       4  p/default/test-pod:42604   r/1.1.1.1:80         70B        381B

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 ig​

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 ig top tcp -c test-top-tcp
RUNTIME.CONTAINERNAME      PID         COMM           IP SRC                               DST                               SENT          RECV
test-top-tcp               2177846     nginx          4  127.0.0.1:80                      127.0.0.1:53130                   238B          73B
test-top-tcp               2178303     curl           4  127.0.0.1:53130                   127.0.0.1:80                      73B           853B