Background

On a recent project, I’ve been troubleshooting some connectivity issues in a Kubernetes cluster. The pods were failing to talk to external on-prem systems and I had to prepare a Minimal, Reproducible Example (MRE) for the network administrators.

In this post, I’ll demonstrate how to start a temporary debug container in a K8S cluster and open up a terminal sessions into it. This will allow us to test various network issues without leaving any permanent pods behind.

The Test Pod & Container

Let’s start by creating a YAML file which defines the test pod:

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apiVersion: v1
kind: Pod
metadata:
  name: testcurl
spec:
  containers:
  - name: curl
    image: curlimages/curl 
    command: [ "sleep", "600" ]

In the above, we’re defining a new pod with a single container based on the curlimages/curl image. This is a minimalistic image (about 11MB) which includes curl - you can obviously choose to use a bigger image with more networking tools.

The container will complete in 10 minutes and the pod will be die/exit. If you need more time for your troubleshooting please increase the sleep interval in the above config.

Let’s create the pod in the cluster:

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kubectl apply -f pod.yaml

After the pod starts, you should be able to open a terminal into the container and execute curl commands:

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# Will open up a terminal session into the container
kubectl exec -it testcurl -- sh

# We can now curl external addresses or internal services:
> curl http://example.com/
> curl myservice/health