The running state of an application can be observed through a variety of kubectl describe commands across various resources.
Inspect the whole cluster
kubectl cluster-info
or more verbose (and really too much)
kubectl cluster-info dump --all-namespaces
Inspect this Kubernetes cluster only Worker node.
kubectl describe node node01
Inspect the last deployment.
kubectl describe deployment random-logger
Specifically, the replica state.
kubectl describe deployments | grep "Replicas:"
Inspect the 3 pods.
kubectl get pods
kubectl describe pods
Events
Kubernetes also maintains a list of events.
kubectl get events
Scaling is a type of event. Scale down the pod from 3 down to 2.
kubectl scale deployment/random-logger --replicas=2
Notice the last event will reflect the scaling request.
kubectl get events --sort-by=.metadata.creationTimestamp
These events are not to be confused with security audit logs which are also recorded.
Inspecting Containers
You can also typically get into a running container and inspect it as well. Get the name of the first Pod.
POD=$(kubectl get pod -o jsonpath="{.items[0].metadata.name}")
Inspect the script contents inside the container file system.
kubectl exec $POD -- cat entrypoint.sh
Or, shell into the container.
kubectl exec -it $POD -- /bin/sh
and come back out with the exit command.
There is a wealth of helpful Linux commands to give you information about the Linux containers. Here are just a few.
kubectl exec $POD -- uptime
kubectl exec $POD -- ps
kubectl exec $POD -- stat -f /
kubectl exec $POD --container random-logger -- lsof
kubectl exec $POD --container random-logger -- iostat
When the Pod has more than one container, the specific container name may be referenced.
kubectl exec $POD --container random-logger -- ls -a -l
