How to understand that an application inside a pod has started?

To understand that the application inside the pod has started, you can use several approaches:

• Checking the container status: the command kubectl get pods will show the pod status. A status of Running and READY with the number of containers equal to the expected is a good sign.
• Container logs: the command kubectl logs <pod-name> allows you to view the application's logs. If the logs contain messages about successful startup or no errors, the application has started.
• Checking Readiness and Liveness probes: if the pod manifest has readinessProbe and livenessProbe configured, Kubernetes will monitor the application's state. The command kubectl describe pod <pod-name> will show the probe statuses.

Example of checking status and logs:

kubectl get pods
kubectl logs <pod-name>
kubectl describe pod <pod-name>

If the application listens on a specific port, you can also execute kubectl exec and check the service's accessibility inside the pod.