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Using trace dns

Screencast of the trace dns gadget

The trace dns gadget prints information about DNS queries and responses sent and received by the different pods.

On Kubernetes​

Create a demo namespace:

$ kubectl create ns demo
namespace/demo created

Start the dns gadget:

$ kubectl gadget trace dns -n demo
K8S.NODE                      K8S.NAMESPACE                 K8S.PODNAME                   QR NAMESERVER      TYPE      QTYPE      NAME

Run a pod on a different terminal and perform some DNS requests:

$ kubectl -n demo run mypod -it --image=wbitt/network-multitool -- /bin/sh
# nslookup -querytype=a inspektor-gadget.io. 8.8.4.4
# nslookup -querytype=aaaa inspektor-gadget.io. 8.8.4.4
# nslookup -querytype=mx inspektor-gadget.io. 8.8.4.4

The requests will be logged by the DNS gadget:

K8S.NODE             K8S.NAMESPACE        K8S.PODNAME          PID         TID         COMM        QR NAMESERVER      TYPE      QTYPE      NAME                RCODE
minikube             demo                 mypod                1285309     1285310     isc-net-00… Q  8.8.4.4         OUTGOING  A          inspektor-gadget.i…
minikube             demo                 mypod                1285309     1285310     isc-net-00… R  8.8.4.4         HOST      A          inspektor-gadget.i… No Error
minikube             demo                 mypod                1285594     1285595     isc-net-00… Q  8.8.4.4         OUTGOING  AAAA       inspektor-gadget.i…
minikube             demo                 mypod                1285594     1285595     isc-net-00… R  8.8.4.4         HOST      AAAA       inspektor-gadget.i… No Error
minikube             demo                 mypod                1285655     1285656     isc-net-00… Q  8.8.4.4         OUTGOING  MX         inspektor-gadget.i…
minikube             demo                 mypod                1285655     1285656     isc-net-00… R  8.8.4.4         HOST      MX         inspektor-gadget.i… No Error

isc-net-0000 is the name of one of the nslookup threads.

Delete the demo test namespace:

$ kubectl delete ns demo
namespace "demo" deleted

With ig​

Let's start the gadget in a terminal:

$ sudo ig trace dns -c test-trace-dns
RUNTIME.CONTAINERNAME                   PID        TID        COMM             QR TYPE      QTYPE      NAME                                   RCODE                NUMANSW…

Launch a container that makes DNS requests:

$ docker run --name test-trace-dns -it --rm wbitt/network-multitool /bin/sh
/ # nslookup -querytype=a inspektor-gadget.io. 8.8.4.4
...
/ # nslookup -querytype=aaaa inspektor-gadget.io. 8.8.4.4
...
/ # nslookup -querytype=mx inspektor-gadget.io. 8.8.4.4
...

The tool will list the different DNS queries that were made:

$ sudo ig trace dns -c test-trace-dns
RUNTIME.CONTAINERNAME                   PID        TID        COMM             QR TYPE      QTYPE      NAME                                   RCODE                NUMANSW…
test-trace-dns                          38797      38798      isc-net-0000     Q  OUTGOING  A          inspektor-gadget.io.                                        0
test-trace-dns                          38797      38798      isc-net-0000     R  HOST      A          inspektor-gadget.io.                   No Error             2
test-trace-dns                          38801      38802      isc-net-0000     Q  OUTGOING  AAAA       inspektor-gadget.io.                                        0
test-trace-dns                          38801      38802      isc-net-0000     R  HOST      AAAA       inspektor-gadget.io.                   No Error             2
test-trace-dns                          38807      38808      isc-net-0000     Q  OUTGOING  MX         inspektor-gadget.io.                                        0
test-trace-dns                          38807      38808      isc-net-0000     R  HOST      MX         inspektor-gadget.io.                   No Error             3

Limitations​