Network policy is not targeting any pod

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Metadata

Id: terraform-kubernetes-network-policy-is-not-targeting-any-pod

Provider: Kubernetes

Platform: Terraform

Severity: Low

Category: Networking and Firewall

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Description

Checks whether any kubernetes_network_policy does not target any pod.
Validates that spec.pod_selector.match_labels contains concrete label key/value pairs that match at least one pod’s metadata.labels and not unresolved references like kubernetes_<resource>.<name>.
If no pod matches the selector or the label value appears to be a reference, the rule reports an IncorrectValue issue.

Compliant Code Examples

resource "kubernetes_network_policy" "example2" {
  metadata {
    name      = "terraform-example-network-policy"
    namespace = "default"
  }

  spec {
    pod_selector {
      match_expressions {
        key      = "name"
        operator = "In"
        values   = ["webfront", "api"]
      }
      match_labels = {
            app = "ngnix2"
      }

    }

    ingress {
      ports {
        port     = "http"
        protocol = "TCP"
      }
      ports {
        port     = "8125"
        protocol = "UDP"
      }

      from {
        namespace_selector {
          match_labels = {
            name = "default"
          }
        }
      }

      from {
        ip_block {
          cidr = "10.0.0.0/8"
          except = [
            "10.0.0.0/24",
            "10.0.1.0/24",
          ]
        }
      }
    }

    egress {} # single empty rule to allow all egress traffic

    policy_types = ["Ingress", "Egress"]
  }
}

resource "kubernetes_pod" "test2" {
  metadata {
    name = "terraform-example"

    labels = {
      app = "ngnix2"
    }
  }

  spec {
    container {
      image = "nginx:1.7.9"
      name  = "example"

      env {
        name  = "environment"
        value = "test"
      }

      port {
        container_port = 8080
      }

      liveness_probe {
        http_get {
          path = "/nginx_status"
          port = 80

          http_header {
            name  = "X-Custom-Header"
            value = "Awesome"
          }
        }

        initial_delay_seconds = 3
        period_seconds        = 3
      }
    }

    dns_config {
      nameservers = ["1.1.1.1", "8.8.8.8", "9.9.9.9"]
      searches    = ["example.com"]

      option {
        name  = "ndots"
        value = 1
      }

      option {
        name = "use-vc"
      }
    }

    dns_policy = "None"
  }
}


resource "kubernetes_network_policy" "example222" {
  metadata {
    name      = "terraform-example-network-policy"
    namespace = "default"
  }

  spec {
    pod_selector {
      match_expressions {
        key      = "name"
        operator = "In"
        values   = ["webfront", "api"]
      }
      match_labels = {
            app = "kubernetes_pod.test2.metadata.0.labels.app"
      }

    }

    ingress {
      ports {
        port     = "http"
        protocol = "TCP"
      }
      ports {
        port     = "8125"
        protocol = "UDP"
      }

      from {
        namespace_selector {
          match_labels = {
            name = "default"
          }
        }
      }

      from {
        ip_block {
          cidr = "10.0.0.0/8"
          except = [
            "10.0.0.0/24",
            "10.0.1.0/24",
          ]
        }
      }
    }

    egress {} # single empty rule to allow all egress traffic

    policy_types = ["Ingress", "Egress"]
  }
}

# Negative: the NetworkPolicy targets pods with `app = "ngnix-v1"`, and a
# matching pod is declared via the current `kubernetes_pod_v1` provider
# resource. `findTargettedPod` must recognize `_v1` pods in addition to
# `kubernetes_pod`.
resource "kubernetes_network_policy" "example_v1" {
  metadata {
    name      = "terraform-example-network-policy-v1"
    namespace = "default"
  }

  spec {
    pod_selector {
      match_labels = {
        app = "ngnix-v1"
      }
    }

    policy_types = ["Ingress"]
  }
}

resource "kubernetes_pod_v1" "test_v1" {
  metadata {
    name = "terraform-example-v1"
    labels = {
      app = "ngnix-v1"
    }
  }

  spec {
    container {
      image = "nginx:1.7.9"
      name  = "example"
    }
  }
}

Non-Compliant Code Examples

resource "kubernetes_network_policy" "example" {
  metadata {
    name      = "terraform-example-network-policy"
    namespace = "default"
  }

  spec {
    pod_selector {
      match_expressions {
        key      = "name"
        operator = "In"
        values   = ["webfront", "api"]
      }
      match_labels = {
            app = "ngnix"
      }

    }

    ingress {
      ports {
        port     = "http"
        protocol = "TCP"
      }
      ports {
        port     = "8125"
        protocol = "UDP"
      }

      from {
        namespace_selector {
          match_labels = {
            name = "default"
          }
        }
      }

      from {
        ip_block {
          cidr = "10.0.0.0/8"
          except = [
            "10.0.0.0/24",
            "10.0.1.0/24",
          ]
        }
      }
    }

    egress {} # single empty rule to allow all egress traffic

    policy_types = ["Ingress", "Egress"]
  }
}

# Reproduces a false-negative scenario: the NetworkPolicy targets pods with
# `app = "ngnix"`, but the only resource in the module that carries a matching
# label is a non-Kubernetes resource (a Teleport app). The rule must still
# flag the NetworkPolicy because no `kubernetes_pod` targets it.
resource "kubernetes_network_policy" "positive2" {
  metadata {
    name      = "terraform-example-network-policy-2"
    namespace = "default"
  }

  spec {
    pod_selector {
      match_labels = {
        app = "ngnix"
      }
    }

    policy_types = ["Ingress"]
  }
}

resource "teleport_app" "decoy" {
  version = "v3"
  metadata = {
    name = "not-a-pod"
    labels = {
      app = "ngnix"
    }
  }

  spec = {
    uri = "tcp://example.com:443"
  }
}