It’s a rare occurrence, but there may be a time when you need to make a direct call to the Kubernetes API server to do something. Or maybe you are just curious about the REST API and what’s happening under the covers!
The Kubernetes docs do a great job on showing the first step how to get the token and curl the API, but how do you start discovering the different API calls for different operations?
The answer is through kubectl. Add verbose logging level of 8+ and you will get the API calls!
Let’s see this in action. Say you want to get the Kubernetes API call to get all of the pods in the default namespace:
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$ kubectl get pods -v=8
The output contains a lot of information:
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I0827 06:51:49.950850 8021 loader.go:375] Config loaded from file: /home/trstringer/.kube/config
I0827 06:51:49.954797 8021 round_trippers.go:420] GET https://myapiserver:443/api/v1/namespaces/default/pods?limit=500
I0827 06:51:49.954817 8021 round_trippers.go:427] Request Headers:
I0827 06:51:49.954821 8021 round_trippers.go:431] Accept: application/json;as=Table;v=v1;g=meta.k8s.io,application/json;as=Table;v=v1beta1;g=meta.k8s.io,application/json
I0827 06:51:49.954826 8021 round_trippers.go:431] User-Agent: kubectl/v1.19.0 (linux/amd64) kubernetes/e199641
I0827 06:51:49.954831 8021 round_trippers.go:431] Authorization: Bearer <masked>
I0827 06:51:50.141125 8021 round_trippers.go:446] Response Status: 200 OK in 186 milliseconds
I0827 06:51:50.141185 8021 round_trippers.go:449] Response Headers:
I0827 06:51:50.141197 8021 round_trippers.go:452] Cache-Control: no-cache, private
I0827 06:51:50.141206 8021 round_trippers.go:452] Content-Type: application/json
I0827 06:51:50.141214 8021 round_trippers.go:452] X-Kubernetes-Pf-Flowschema-Uid: ac1def70-6b11-457d-a19a-79b2e24d3a65
I0827 06:51:50.141226 8021 round_trippers.go:452] X-Kubernetes-Pf-Prioritylevel-Uid: 954e3926-9429-459a-bdc3-267ebd39a141
I0827 06:51:50.141309 8021 round_trippers.go:452] Content-Length: 2880
I0827 06:51:50.141328 8021 round_trippers.go:452] Date: Fri, 27 Aug 2021 10:51:50 GMT
I0827 06:51:50.141334 8021 round_trippers.go:452] Audit-Id: dc2bcab3-534e-45d5-8eea-aec00874df07
I0827 06:51:50.141381 8021 request.go:1097] Response Body: {"kind":"Table","apiVersion":"meta.k8s.io/v1","metadata":{"resourceVersion":"2035"},"columnDefinitions":[{"name":"Name","type":"string","format":"name","description":"Name must be unique within a namespace. Is required when creating resources, although some resources may allow a client to request the generation of an appropriate name automatically. Name is primarily intended for creation idempotence and configuration definition. Cannot be updated. More info: http://kubernetes.io/docs/user-guide/identifiers#names","priority":0},{"name":"Ready","type":"string","format":"","description":"The aggregate readiness state of this pod for accepting traffic.","priority":0},{"name":"Status","type":"string","format":"","description":"The aggregate status of the containers in this pod.","priority":0},{"name":"Restarts","type":"integer","format":"","description":"The number of times the containers in this pod have been restarted.","priority":0},{"name":"Age","type":"string","format":"","description":"CreationTimestamp is a [truncated 1856 chars]
No resources found in default namespace.
We see a lot of interesting things here, but we are curious about the API call which we can find on the second line. So now we know the API call to get all pods in the default namespace is a GET on api/v1/namespaces/default/pods.
Let’s see another example: Find all services in the cluster with the label component=apiserver.
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$ kubectl get services --all-namespaces -l component=apiserver -v=8
Looking through the output we can see that the API call is a GET on api/v1/services?labelSelector=component%3Dapiserver.
What about if you want to create or modify a Kubernetes resource? You can still do the same thing as above, but there’s a good chance you don’t want kubectl doing the creation or modification. You might just want kubectl to tell you the API call, but don’t do it. We can add the parameter --dry-run=server to get this information without modifying anything!
Another example: Find out the API call to create a namespace, without creating the namespace.
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$ kubectl create namespace test --dry-run=server -v=8
We can see with the output that it is a POST on api/v1/namespaces with the request body of {"apiVersion":"v1","kind":"Namespace","metadata":{"creationTimestamp":null,"name":"test"},"spec":{},"status":{}}.
And since this was a dry run, the namespace wasn’t created.
Hopefully this blog post has showed you a quick and easy way to get the Kubernetes API calls for any operation you can run through kubectl!