Add kubectl frequently used commands

kubernetes/KUBECTL_FAQ.md

@@ -0,0 +1,35 @@
+# Tips for working with kubernetes
+
+## Show all pods in all namespaces
+
+```shell
+kubectl get pods --all-namespaces
+```
+
+(you can use `-A` instead of `--all-namespaces`)
+
+## Show resource usage of all pods in all namespaces
+
+```shell
+kubectl top pods --all-namespaces --sum=true
+```
+
+If you want to see resource usage with container granularity, add `--containers=true`:
+
+```shell
+kubectl top pods --all-namespaces --containers=true
+```
+
+## Show resource usage of all nodes
+
+```shell
+$ kubectl top nodes
+NAME           CPU(cores)   CPU%   MEMORY(bytes)   MEMORY%
+pp-hetzner01   4250m        35%    53130Mi         82%
+```
+
+## Show resource limits and requests for all pods in all namespaces
+
+```shell
+kubectl get pods -o "custom-columns=NAMESPACE:.metadata.namespace,NAME:.metadata.name,MEMORY_REQUESTS:.spec.containers[*].resources.requests.memory,MEMORY_LIMITS:.spec.containers[*].resources.limits.memory,CPU_REQUESTS:.spec.containers[*].resources.requests.cpu,CPU_LIMITS:.spec.containers[*].resources.limits.cpu" -A | sort
+```

kubernetes/README.md

@@ -165,6 +165,8 @@ See [kubeconfig docs](https://kubernetes.io/docs/concepts/configuration/organize
 
 ## Tips
 
+You can find frequently used `kubectl` commands in the [KUBECTL_FAQ.md](./KUBECTL_FAQ.md) file.
+
 ### Debugging failed deployments with kubectl
 
 If a deployment fails, you can use `kubectl` to get more information. For example, to see the status of the pods: