From 706b6092a16be5e9aee0f8ad8246416f648abb1a Mon Sep 17 00:00:00 2001
From: Przemek Maciolek <pmaciolek@sumologic.com>
Date: Sat, 21 Mar 2020 11:21:18 +0100
Subject: [PATCH] Extract hostname from pod.name when the former is not set

---
 processor/k8sprocessor/kube/client.go      |  9 +++++++-
 processor/k8sprocessor/kube/client_test.go | 25 ++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/processor/k8sprocessor/kube/client.go b/processor/k8sprocessor/kube/client.go
index 49a731074d41..05668d8cca4e 100644
--- a/processor/k8sprocessor/kube/client.go
+++ b/processor/k8sprocessor/kube/client.go
@@ -222,7 +222,14 @@ func (c *WatchClient) extractPodAttributes(pod *api_v1.Pod) map[string]string {
 	}
 
 	if c.Rules.HostName {
-		tags[c.Rules.Tags.HostName] = pod.Spec.Hostname
+		// Basing on v1.17 Kubernetes docs, when a hostname is specified, it takes precedence over
+		// the associated metadata name, see:
+		// https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/#pod-s-hostname-and-subdomain-fields
+		if pod.Spec.Hostname == "" {
+			tags[c.Rules.Tags.HostName] = pod.Name
+		} else {
+			tags[c.Rules.Tags.HostName] = pod.Spec.Hostname
+		}
 	}
 
 	if c.Rules.ClusterName {
diff --git a/processor/k8sprocessor/kube/client_test.go b/processor/k8sprocessor/kube/client_test.go
index 76d438947447..0cfb140e12d5 100644
--- a/processor/k8sprocessor/kube/client_test.go
+++ b/processor/k8sprocessor/kube/client_test.go
@@ -125,6 +125,31 @@ func TestDeleteQueue(t *testing.T) {
 	// test delete loop
 }
 
+func TestNoHostnameExtractionRules(t *testing.T) {
+	c := newTestClientWithRulesAndFilters(t, ExtractionRules{}, Filters{})
+
+	podName := "auth-service-abc12-xyz3"
+
+	pod := &api_v1.Pod{
+		ObjectMeta: meta_v1.ObjectMeta{
+			Name: podName,
+		},
+		Spec: api_v1.PodSpec{},
+		Status: api_v1.PodStatus{
+			PodIP: "1.1.1.1",
+		},
+	}
+
+	c.Rules = ExtractionRules{
+		HostName: true,
+		Tags:     NewExtractionFieldTags(),
+	}
+
+	c.handlePodAdd(pod)
+	p, _ := c.GetPodByIP(pod.Status.PodIP)
+	assert.Equal(t, p.Attributes["k8s.pod.hostname"], podName)
+}
+
 func TestExtractionRules(t *testing.T) {
 	c := newTestClientWithRulesAndFilters(t, ExtractionRules{}, Filters{})