Yuvi Panda

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Kubectl verbose logging tricks

Recently I had to write some code that had to call the kubernetes API directly, without any language wrappers. While there is pretty good reference docs, I didn’t want to go and construct all the JSON manually in my programming language.

I discovered that kubectl’s -v parameter is very useful for this! With this, I can do the following:

  1. Perform the actions I need to perform with just kubectl commands
  2. Pass -v=8 to kubectl when doing this, and this will print all the HTTP traffic (requests and responses!) in an easy to read way
  3. Copy paste the JSON requests and template them as needed!

This was very useful! The fact you can see the response bodies is also nice, since it gives you a good intuition of how to handle this in your own code.

If you’re shelling out to kubectl directly in your code (for some reason!), you can also use this to figure out all the RBAC rules your code would need. For example, if I’m going to run the following in my script:

kubectl get node

and need to figure out which RBAC rules are needed for this, I can run:

kubectl -v=8 get node 2>&1 | grep -P 'GET|POST|DELETE|PATCH|PUT'

This should list all the API requests the code is making, making it easier to figure out what rules are needed.

Note that you might have to rm -rf ~/.kube/cache to ‘really’ get the full API requests list, since kubectl caches a bunch of API autodiscovery. The minimum RBAC for kubectl is:

kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1beta1
metadata:
  name: kubectl-minimum
rules:
- nonResourceURLs: ["/api", "/apis/*"]
  verbs: ["get"]

You will need to add additional rules for the specific commands you want to execute.

More Kubectl Tips

  1. Slides from the ‘Stupid Kubectl Tricks’ KubeCon talk
  2. On the CoreOS blog
  3. Terse but useful official documentation