I have a pod that exposes a port (Server). Other pods (Clients) can communicate with it.
The server can find remote IP and port on a socket (when the client connects to it). I am looking for a way to get the client's pod name (from its IP and port).
I saw a bunch of questions/answers about getting pod names via kubectl. However, I am not sure whether I can do kubectl from within a cluster itself.
I am trying to figure out what is available for something running on the cluster. It's ok if it requires some special privileges. It's more complicated if it requires authentication.
List all the Pods with the List Pods API operation and parse the JSON response for the podIP field (e.g. with jq or some other JSON parsing tool) to find the JSON object of the Pod that has your desired IP address. Then, extract the metadata.name field from this JSON object to get the name of the Pod.
You can do this by either directly using the Kubernetes API (e.g. with curl) or with kubectl (e.g. kubectl get pods -o json | jq ...). In any case, you must include in this request the ServiceAccount token of the ServiceAccount used by the Pod from which you are issuing the request (if you use the Kubernetes API directly, as a Bearer token in the Authorization header, and if you use kubectl with the --token command-line flag).
Regarding authorisation, you need a Role allowing the list verb on the pods resource and a RoleBinding that binds this Role to the ServiceAccount that your Pod is using (by default, Pods use a ServiceAccount named default in their namespace, but you can specify a custom ServiceAccount with the serviceAccountName field of the Pod).
Whatever can be done via kubectl can be done via direct requests to the API server as well. All you need is to have proper ServiceAccount set up for your pod. Once you have it - you use can plenty of libraries dedicated for communication with k8s API server.