Missing kube_inventory metrics when Pod has no valid containers

[Fiery-Fenix]

Relevant telegraf.conf:

[[inputs.kube_inventory]]
interval = "30s"
url = "https://kubernetes.default"
namespace = ""
insecure_skip_verify = true

System info:

Telegraf version 1.15.2

Steps to reproduce:

On Kubernetes cluster one of Pods was manually restarted and we didn't receive any metrics that can indicate that restart because telegraf has take metrics directly in the moment when no valid containers were in v1.Pod.Status.ContainerStatuses.
Respective piece of code:

for i, cs := range p.Status.ContainerStatuses {
	c := p.Spec.Containers[i]
	gatherPodContainer(*p.Spec.NodeName, ki, p, *cs, *c, acc)
}

For some valid reasons (for example Network issues) it could be that p.Status.ContainerStatuses is empty and we will not receive any metrics at all until issue will be resolved, as in above example of restarting Pod.

Expected behavior:

kubernetes_pod_container,container_name=telegraf,namespace=default,node_name=ip-172-17-0-2.internal,node_selector_node-role.kubernetes.io/compute=true,pod_name=tick1,state=running,readiness=ready resource_requests_cpu_units=0.1,resource_limits_memory_bytes=524288000,resource_limits_cpu_units=0.5,restarts_total=0i,state_code=0i,state_reason="",resource_requests_memory_bytes=524288000 1547597616000000000
kubernetes_pod_container,container_name=telegraf,namespace=default,node_name=ip-172-17-0-2.internal,node_selector_node-role.kubernetes.io/compute=true,pod_name=tick1,state=unknown,readiness=unready resource_requests_cpu_units=0.1,resource_limits_memory_bytes=524288000,resource_limits_cpu_units=0.5,restarts_total=0i,state_code=3i,state_reason="",resource_requests_memory_bytes=524288000 1547597916000000000
kubernetes_pod_container,container_name=telegraf,namespace=default,node_name=ip-172-17-0-2.internal,node_selector_node-role.kubernetes.io/compute=true,pod_name=tick1,state=unknown,readiness=ready resource_requests_cpu_units=0.1,resource_limits_memory_bytes=524288000,resource_limits_cpu_units=0.5,restarts_total=0i,state_code=0i,state_reason="",resource_requests_memory_bytes=524288000 1547598516000000000

Actual behavior:

kubernetes_pod_container,container_name=telegraf,namespace=default,node_name=ip-172-17-0-2.internal,node_selector_node-role.kubernetes.io/compute=true,pod_name=tick1,state=running,readiness=ready resource_requests_cpu_units=0.1,resource_limits_memory_bytes=524288000,resource_limits_cpu_units=0.5,restarts_total=0i,state_code=0i,state_reason="",resource_requests_memory_bytes=524288000 1547597616000000000
kubernetes_pod_container,container_name=telegraf,namespace=default,node_name=ip-172-17-0-2.internal,node_selector_node-role.kubernetes.io/compute=true,pod_name=tick1,state=unknown,readiness=ready resource_requests_cpu_units=0.1,resource_limits_memory_bytes=524288000,resource_limits_cpu_units=0.5,restarts_total=0i,state_code=0i,state_reason="",resource_requests_memory_bytes=524288000 1547598516000000000

Additional info:

PR: #8472

[akrantz01]

Already fixed by #8472.