Missing .spec.serviceName in the Thanos Ruler statefulset

[simonpasquier]

What happened?

• Deploy a ThanosRuler resource named foo in namespace default with 1 replica.
• Resolve the thanos-ruler-foo-0.thanos-operated.default.cluster.local` name inside the Thanos ruler container.

The name can't be resolved.

Did you expect to see something different?

The name should be resolved to the IP of the pod.

How to reproduce it (as minimally and precisely as possible):

See above.

Environment

• Prometheus Operator version: main

• Kubernetes version information: N/A

• Kubernetes cluster kind: N/A

• Manifests: N/A

• Prometheus Operator Logs: N/A

Anything else we need to know?:

The operator doesn't set the .spec.serviceName to thanos-operator in the statefulset.

Though the Kubernetes documentation states that service name is mandatory, an empty value is valid (see kubernetes/kubernetes#69608) hence we didn't catch it before. In practice, it only causes an issue if you want to resolve the IP address of an individual pod but to configure a Thanos query, you would use the DNSSRV records of the service which return the expected result.

[simonpasquier]

the fix is to add ServiceName: governingServiceName in this block

prometheus-operator/pkg/thanos/statefulset.go

Lines 440 to 470 in 54ed924

	return &appsv1.StatefulSetSpec{
	Replicas: tr.Spec.Replicas,
	MinReadySeconds: minReadySeconds,
	PodManagementPolicy: appsv1.ParallelPodManagement,
	UpdateStrategy: appsv1.StatefulSetUpdateStrategy{
	Type: appsv1.RollingUpdateStatefulSetStrategyType,
	},
	Selector: &metav1.LabelSelector{
	MatchLabels: finalLabels,
	},
	Template: v1.PodTemplateSpec{
	ObjectMeta: metav1.ObjectMeta{
	Labels: finalLabels,
	Annotations: podAnnotations,
	},
	Spec: v1.PodSpec{
	NodeSelector: tr.Spec.NodeSelector,
	PriorityClassName: tr.Spec.PriorityClassName,
	ServiceAccountName: tr.Spec.ServiceAccountName,
	TerminationGracePeriodSeconds: &terminationGracePeriod,
	Containers: containers,
	InitContainers: tr.Spec.InitContainers,
	Volumes: trVolumes,
	SecurityContext: tr.Spec.SecurityContext,
	Tolerations: tr.Spec.Tolerations,
	Affinity: tr.Spec.Affinity,
	TopologySpreadConstraints: tr.Spec.TopologySpreadConstraints,
	HostAliases: operator.MakeHostAliases(tr.Spec.HostAliases),
	},
	},
	}, nil