Check working of an service in kubernetes - kubernetes

Question

I create a pod to test my service in kubernetes. But i didn't get anythings. Here is my command
kubectl run --generator=run-pod/v1 nginx-resolver --image=nginx
kubectl expose pod nginx-resolver --name=nginx-resolver-service --port=80 --target-port=80 --type=ClusterIP
kubectl run --generator=run-pod/v1 test-nslookup --image=busybox:1.28 --rm -it -- nslookup nginx-resolver-service
Please help me explain why. Thanks

Answer 1

Run the following command and get things what you are thinking wrong about this cmd.
$ kubectl run --help
Create and run a particular image, possibly replicated.
Creates a deployment or job to manage the created container(s).
Examples:
# Start a single instance of nginx.
kubectl run nginx --image=nginx
# Start a single instance of hazelcast and let the container expose port 5701 .
kubectl run hazelcast --image=hazelcast --port=5701
...
So, kubectl run cmd creates a deployment or a job
If it is a deployment, it creates (a) first, a replicaset, (b) then Pod(s).
If it is a job, it creates a Pod.
But you are trying to expose a Pod which name is not the correct one. You can see the name of the Pod that is/are created by the cmd kubectl run.
$ kubectl get pods --namespace=<namespace> | grep "nginx-resolver"
$ kubectl get pods --namespace=<namespace> | grep "test-nslookup"
Then use those names to expose Pod.
You can optionally expose your Deployment. To do so, see the help of $ kubectl expose deployment --help. Run:
$ kubectl expose deployment --help
Expose a resource as a new Kubernetes service.
Looks up a deployment, service, replica set, replication controller or pod by name and uses the selector for that
resource as the selector for a new service on the specified port. A deployment or replica set will be exposed as a
service only if its selector is convertible to a selector that service supports, i.e. when the selector contains only
the matchLabels component. Note that if no port is specified via --port and the exposed resource has multiple ports, all
will be re-used by the new service. Also if no labels are specified, the new service will re-use the labels from the
resource it exposes.
Possible resources include (case insensitive):
pod (po), service (svc), replicationcontroller (rc), deployment (deploy), replicaset (rs)
Examples:
...
# Create a service for an nginx deployment, which serves on port 80 and connects to the containers on port 8000.
kubectl expose deployment nginx --port=80 --target-port=8000
...

Answer 2

If you want to see the log interactively, you need to set the --restart option of your test-nslookup pod to Never or OnFailure. Otherwise, kubernetes will just restart your pod indefinitely and you won't see anything.
So your last command should be :
kubectl run --generator=run-pod/v1 test-nslookup --image=busybox:1.28 -it --restart=OnFailure -- nslookup nginx-resolver-service
Why ?
Probably because of this issue.
It seems to have a delay of 5s before kubectl run actually print something.
So in order to do it without changing the restart option, you'll need to change your command like this (beware of the sleep 7, so you'll have to wait 7seconds before seeing the logs) :
kubectl run --generator=run-pod/v1 test-nslookup --image=busybox:1.28 -it --rm -- sh -c 'sleep 7; nslookup nginx-resolver-service'