sionsmith/nc-pod

nc-pod

A simple https://kubernetes.io/ https://kubernetes.io/docs/user-guide/pods/ that runs http://netcat.sourceforge.net/ (nc) typically in the role of the listening endpoint.

The goal of this simple little Pod is to enable any number of Kubernetes networking configuration test scenarios. From a simple intra-pod connectivity test (show here), to any form of advanced networking configuration you can apply to Kubernetes Pods and more specifially, https://kubernetes.io/docs/user-guide/services/.

Building the Docker Image

Build and push the docker image, replacing the Samsung private Quay registry with your target registry.

$ docker build --rm --tag quay.io/samsung_cnct/nc-pod .
$ docker push quay.io/samsung_cnct/nc-pod:latest

Helm Chart

This project might also end up being packaged as a Helm Chart eventually.
However, it's pretty dead simple as is, and might not need to ever become a chart... we'll see.

Configuration

Configuring 'nc' execution is handled by a single environment variable that captures the entire set of 'nc' command line arguments, but not the 'nc' command itself.

For a complete description of 'nc' command line arguments see: man nc(1)

Environment Variable:

• NC_CMD_ARGS: Required, a quoted string of nc command line arguments.

Example (excerpt from https://kubernetes.io/docs/user-guide/deployments/#writing-a-deployment-spec yaml):

    spec:
      containers:
      - name: nc-pod
        image: quay.io/samsung_cnct/nc-pod
        env:
        - name: NC_CMD_ARGS
          value: "-lk -n -u -p 26500"

Deployment

Using the example nc-pod.yaml file's default values, the project is easily deployed as shown here:

$ kubectl create -f nc-pod.yaml
deployment "nc-pod" created

$ kubectl expose -f nc-pod.yaml 
service "nc-pod" exposed

$ kubectl get po,ep -l app=nc-pod
NAME                         READY     STATUS    RESTARTS   AGE
po/nc-pod-2355685321-3gd8r   1/1       Running   0          58s

NAME        ENDPOINTS          AGE
ep/nc-pod   10.64.0.23:26500   48s

Running / Testing with netcat

From the example https://kubernetes.io/docs/user-guide/deployments/ above we tail the output of the created pod.

$ kubectl logs -f nc-pod-2355685321-3gd8r
cmd: /bin/nc -lk -n -u -p 26500 

We'll check back on the output of the 'logs' command after the next steps.

Since the service created by the default example isn't exposed via a public IP address, we need to login to either a cluster node or pod. Let's stay away from using the node, and stick to a pod.

$ kubectl run -i -t alps --image=alpine:latest --restart=Never --command /bin/ash
Waiting for pod default/alps to be running, status is Pending, pod ready: false
If you don't see a command prompt, try pressing enter.
/ # 
/ # nc -n -u 10.64.0.23 26500
Example of running netcat in a pod.
^Cpunt!

/ # exit
$ 

As soon as we hit ruturn on our input line above, we should have seen the following output scroll in our 'logs -f' terminal:

rastop:nc-pod sostheim$ kubectl logs -f nc-pod-2355685321-3gd8r
cmd: /bin/nc -lk -n -u -p 26500 
Example of running netcat in a pod.