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Check pod-exists

Check command pod-exists is used to check existence of pods in a Kubernetes cluster.

Spec

pod-exists has the following variables:

• selector - Label selector for pods whose existence are checked.
• podName - Name of Kubernetes pod whose existence is checked.
• count - Number of expected Kubernetes pods

Execution of this command can result in following states:

• OK
• Critical
• Unknown

Tutorial

Before You Begin

At first, you need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube.

Now, install Searchlight operator in your cluster following the steps here.

To keep things isolated, this tutorial uses a separate namespace called demo throughout this tutorial. Run the following command to prepare your cluster for this tutorial:

$ kubectl create namespace demo
namespace "demo" created

$ kubectl get namespaces
NAME          STATUS    AGE
default       Active    6h
kube-public   Active    6h
kube-system   Active    6h
demo          Active    4m

Check existence of pods with matching labels

In this tutorial, a ClusterAlert will be used check existence of pods with matching labels by setting spec.vars.selector field.

$ cat ./docs/examples/cluster-alerts/pod-exists/demo-0.yaml

apiVersion: monitoring.appscode.com/v1alpha1
kind: ClusterAlert
metadata:
  name: pod-exists-demo-0
  namespace: demo
spec:
  check: pod-exists
  vars:
    selector: app=nginx
    count: '2'
  checkInterval: 30s
  alertInterval: 2m
  notifierSecretName: notifier-config
  receivers:
  - notifier: Mailgun
    state: Critical
    to: ["ops@example.com"]

$ kubectl apply -f ./docs/examples/cluster-alerts/pod-exists/demo-0.yaml
replicationcontroller "nginx" created
clusteralert "pod-exists-demo-0" created

$ kubectl describe clusteralert -n demo pod-exists-demo-0
Name:		pod-exists-demo-0
Namespace:	demo
Labels:		<none>
Events:
  FirstSeen	LastSeen	Count	From			SubObjectPath	Type		Reason		Message
  ---------	--------	-----	----			-------------	--------	------		-------
  19s		19s		1	Searchlight operator			Warning		BadNotifier	Bad notifier config for ClusterAlert: "pod-exists-demo-0". Reason: secrets "notifier-config" not found
  19s		19s		1	Searchlight operator			Normal		SuccessfulSync	Applied ClusterAlert: "pod-exists-demo-0"

Voila! pod-exists command has been synced to Icinga2. Please visit here to learn how to configure notifier secret. Now, open IcingaWeb2 in your browser. You should see a Icinga host demo@cluster and Icinga service pod-exists-demo-0.

Check existence of a specific pod

In this tutorial, a ClusterAlert will be used check existence of a pod by name by setting spec.vars.podName field.

$ cat ./docs/examples/cluster-alerts/pod-exists/demo-1.yaml

apiVersion: monitoring.appscode.com/v1alpha1
kind: ClusterAlert
metadata:
  name: pod-exists-demo-1
  namespace: demo
spec:
  check: pod-exists
  vars:
    podName: busybox
    count: '1'
  checkInterval: 30s
  alertInterval: 2m
  notifierSecretName: notifier-config
  receivers:
  - notifier: Mailgun
    state: Critical
    to: ["ops@example.com"]

$ kubectl apply -f ./docs/examples/cluster-alerts/pod-exists/demo-1.yaml
pod "busybox" created
podalert "pod-exists-demo-1" created

$ kubectl get pods -n demo
NAME          READY     STATUS    RESTARTS   AGE
busybox       1/1       Running   0          5s

$ kubectl describe podalert -n demo pod-exists-demo-1
Name:		pod-exists-demo-1
Namespace:	demo
Labels:		<none>
Events:
  FirstSeen	LastSeen	Count	From			SubObjectPath	Type		Reason		Message
  ---------	--------	-----	----			-------------	--------	------		-------
  31s		31s		1	Searchlight operator			Warning		BadNotifier	Bad notifier config for ClusterAlert: "pod-exists-demo-1". Reason: secrets "notifier-config" not found
  31s		31s		1	Searchlight operator			Normal		SuccessfulSync	Applied ClusterAlert: "pod-exists-demo-1"
  27s		27s		1	Searchlight operator			Normal		SuccessfulSync	Applied ClusterAlert: "pod-exists-demo-1"

Pause Alert

To pause alert, edit ClusterAlert pod-exists-demo-1 to set spec.paused to be true

$ kubectl edit clusteralert pod-exists-demo-1 -n demo

spec:
  pause: true

Searchlight operator will delete Icinga Services for this alert. To resume, edit and set spec.paused to be false

Cleaning up

To cleanup the Kubernetes resources created by this tutorial, run:

$ kubectl delete ns demo

If you would like to uninstall Searchlight operator, please follow the steps here.

Next Steps

• To periodically run various checks on nodes in a Kubernetes cluster, use NodeAlerts.
• To periodically run various checks on pods in a Kubernetes cluster, use PodAlerts.
• See the list of supported notifiers here.
• Wondering what features are coming next? Please visit here.
• Want to hack on Searchlight? Check our contribution guidelines.