Review the StatefulSet headless Service association

Description

A StatefulSet references a headless Service through spec.service_name to provide stable network names for its pods. Configure cluster_ip = "None" on a Service in the same namespace, with a selector matching the actual pod labels.

Referring to an ordinary Service or an incorrect selector can prevent the expected per-pod DNS names and peer discovery from working.

Potential impact

Peers may be unreachable through stable pod DNS names.
Unreliable discovery during restarts or scaling can complicate recovery of stateful applications.

Remediation

Point the StatefulSet’s service_name to a headless Service in the same namespace and set the Service’s cluster_ip to "None".
Verify the Service selector against actual pod labels, ports and DNS responses. Create the Service separately.

Examples

These excerpts show the Service association only; the required pod template, Service ports and other settings are omitted. The before excerpt omits cluster_ip for ordinary ClusterIP allocation, while the after excerpt selects a headless Service.

Before

hcl

resource "kubernetes_service" "example" {
  metadata {
    name      = "prometheus"
    namespace = "monitoring"
  }

  spec {
    selector = {
      app = "prometheus"
    }
  }
}

resource "kubernetes_stateful_set" "example" {
  metadata {
    name      = "prometheus"
    namespace = "monitoring"
  }

  spec {
    service_name = "prometheus"

    selector {
      match_labels = {
        app = "prometheus"
      }
    }
  }
}

After

hcl

resource "kubernetes_service" "example" {
  metadata {
    name      = "prometheus"
    namespace = "monitoring"
  }

  spec {
    cluster_ip = "None"

    selector = {
      app = "prometheus"
    }
  }
}

resource "kubernetes_stateful_set" "example" {
  metadata {
    name      = "prometheus"
    namespace = "monitoring"
  }

  spec {
    service_name = "prometheus"

    selector {
      match_labels = {
        app = "prometheus"
      }
    }
  }
}

Explanation:

Before: The StatefulSet references an ordinary ClusterIP Service, not a headless Service.
After: cluster_ip is set to None. The omitted pod template must also carry labels matching the selector.