Using snapshot socket

The snapshot socket gadget gathers information about TCP and UDP sockets.

On Kubernetes

We will start this demo by using nginx to create a web server on port 80:

$ kubectl create ns test-socketcollector
namespace/test-socketcollector created
$ kubectl run --restart=Never -n test-socketcollector --image=nginx nginx-app --port=80
pod/nginx-app created

Wait for the pod to get ready:

$ kubectl wait --timeout=-1s -n test-socketcollector --for=condition=ready pod/nginx-app ; kubectl get pod -n test-socketcollector
pod/nginx-app condition met
NAME        READY   STATUS    RESTARTS   AGE
nginx-app   1/1     Running   0          46s

We will now use the snapshot socket gadget to retrieve the TCP/UDP sockets information of the nginx-app pod. Notice we are filtering by namespace but we could have done it also using the podname or labels:

$ kubectl gadget snapshot socket -n test-socketcollector
NODE       NAMESPACE               POD          PROTOCOL    LOCAL         REMOTE       STATUS
my-node    test-socketcollector    nginx-app    TCP         0.0.0.0:80    0.0.0.0:0    LISTEN

In the output, “LOCAL” is the local IP address and port number pair. If connected, “REMOTE” is the remote IP address and port number pair, otherwise, it will be “0.0.0.0:0”. While “STATUS” is the internal status of the socket.

Now, modify the nginx configuration to listen on port 8080 instead of 80 and reload the daemon:

$ kubectl exec -n test-socketcollector nginx-app -- /bin/bash -c "sed -i 's/listen \+80;/listen\t8080;/g' /etc/nginx/conf.d/default.conf && exec nginx -s reload"
[...] signal process started

Now, we can check again with the snapshot socket gadget what the active socket is:

$ kubectl gadget snapshot socket -n test-socketcollector
NODE       NAMESPACE               POD          PROTOCOL    LOCAL           REMOTE       STATUS
my-node    test-socketcollector    nginx-app    TCP         0.0.0.0:8080    0.0.0.0:0    LISTEN

To get extended information, like the socket inode number, just the -e or --extend flag:

$ kubectl gadget snapshot socket -n test-socketcollector -e
NODE       NAMESPACE               POD          PROTOCOL    LOCAL           REMOTE       STATUS         INODE
my-node    test-socketcollector    nginx-app    TCP         0.0.0.0:8080    0.0.0.0:0    LISTEN         716174

Delete test namespace:

$ kubectl delete ns test-socketcollector
namespace "test-socketcollector" deleted

With local-gadget

The snapshot socket is not available on local-gadget yet. Please check https://github.com/inspektor-gadget/inspektor-gadget/issues/744 .