add_kubernetes_metadata supports '/var/log/containers/' log path

The add_kubernetes_metadata processor's LogPathMatcher could extract
a Docker container ID - and hence enrich a log document with Kubernetes
metadata - only if the log path was '/var/lib/docker/containers/'.

With this commit, the LogPathMatcher can extract the container ID also
from a '/var/log/containers/' log path (Kubernetes symlinks).

CHANGELOG.asciidoc

@@ -85,6 +85,7 @@ https://github.com/elastic/beats/compare/v6.0.0-beta1...master[Check the HEAD di
 
 - Add PostgreSQL module with slowlog support. {pull}4763[4763]
 - Add Kafka log module. {pull}4885[4885]
+- Add support for `/var/log/containers/` log path in `add_kubernetes_metadata` processor. {pull}5011[5011]
 
 *Heartbeat*
 

filebeat/processor/add_kubernetes_metadata/indexing.go

@@ -46,20 +46,44 @@ func newLogsPathMatcher(cfg common.Config) (add_kubernetes_metadata.Matcher, err
 	return &LogPathMatcher{LogsPath: logPath}, nil
 }
 
+// Docker container ID is a 64-character-long hexadecimal string
+const containerIdLen = 64
+
+// Minimum `source` lengths are calculated in order to prevent "slice bound out of range"
+// runtime errors in case `source` is shorter than expected.
+const kubernetesLogPath = "/var/log/containers/"
+const kubernetesMinSourceLen = len(kubernetesLogPath) + containerIdLen + 4
+
+const dockerLogPath = "/var/lib/docker/containers/"
+const dockerLogPathLen = len(dockerLogPath)
+const dockerMinSourceLen = dockerLogPathLen + containerIdLen
+
 func (f *LogPathMatcher) MetadataIndex(event common.MapStr) string {
 	if value, ok := event["source"]; ok {
 		source := value.(string)
-		logp.Debug("kubernetes", "Incoming source value: ", source)
-		cid := ""
-		if strings.Contains(source, f.LogsPath) {
-			//Docker container is 64 chars in length
-			cid = source[len(f.LogsPath) : len(f.LogsPath)+64]
+		logp.Debug("kubernetes", "Incoming source value: %s", source)
+
+		sourceLen := len(source)
+
+		// Variant 1: Kubernetes log path "/var/log/containers/...-${cid}.log"
+		if strings.HasPrefix(source, kubernetesLogPath) &&
+		   strings.HasSuffix(source, ".log") &&
+		   sourceLen >= kubernetesMinSourceLen {
+			containerIdEnd := sourceLen - 4
+			cid := source[containerIdEnd - containerIdLen : containerIdEnd]
+			logp.Debug("kubernetes", "Using container id: %s", cid)
+			return cid;
 		}
-		logp.Debug("kubernetes", "Using container id: ", cid)
 
-		if cid != "" {
-			return cid
+		// Variant 2: Docker log path "/var/lib/docker/containers/${cid}/${cid}-json.log"
+		if strings.HasPrefix(source, dockerLogPath) &&
+		   sourceLen >= dockerMinSourceLen {
+			cid := source[dockerLogPathLen : dockerLogPathLen + containerIdLen]
+			logp.Debug("kubernetes", "Using container id: %s", cid)
+			return cid;
 		}
+
+		logp.Debug("kubernetes", "No container id found in source.")
 	}
 
 	return ""

filebeat/processor/add_kubernetes_metadata/indexing_test.go

@@ -9,24 +9,47 @@ import (
 	"github.com/elastic/beats/libbeat/common"
 )
 
-func TestLogsPathMatcher(t *testing.T) {
-	var testConfig = common.NewConfig()
+// A random container ID that we use for our tests
+const cid = "0069869de9adf97f574c62029aeba65d1ecd85a2a112e87fbc28afe4dec2b843"
+
+func TestLogsPathMatcher_InvalidSource1(t *testing.T) {
+	source := "/var/log/messages"
+	expectedResult := ""
+	executeTest(t, source, expectedResult);
+}
+
+func TestLogsPathMatcher_InvalidSource2(t *testing.T) {
+	source := "/var/lib/docker/containers/01234567/89abcdef-json.log"
+	expectedResult := ""
+	executeTest(t, source, expectedResult);
+}
+
+func TestLogsPathMatcher_InvalidSource3(t *testing.T) {
+	source := "/var/log/containers/pod_ns_container_01234567.log"
+	expectedResult := ""
+	executeTest(t, source, expectedResult);
+}
+
+func TestLogsPathMatcher_VarLibDockerContainers(t *testing.T) {
+	source := fmt.Sprintf("/var/lib/docker/containers/%s/%s-json.log", cid, cid)
+	expectedResult := cid;
+	executeTest(t, source, expectedResult);
+}
+
+func TestLogsPathMatcher_VarLogContainers(t *testing.T) {
+	source := fmt.Sprintf("/var/log/containers/kube-proxy-4d7nt_kube-system_kube-proxy-%s.log", cid)
+	expectedResult := cid;
+	executeTest(t, source, expectedResult);
+}
 
+func executeTest(t *testing.T, source string, expectedResult string) {
+	var testConfig = common.NewConfig()
 	logMatcher, err := newLogsPathMatcher(*testConfig)
 	assert.Nil(t, err)
 
-	cid := "0069869de9adf97f574c62029aeba65d1ecd85a2a112e87fbc28afe4dec2b843"
-	logPath := fmt.Sprintf("/var/lib/docker/containers/%s/%s-json.log", cid, cid)
-
 	input := common.MapStr{
-		"source": "/var/log/messages",
+		"source": source,
 	}
-
 	output := logMatcher.MetadataIndex(input)
-	assert.Equal(t, output, "")
-
-	input["source"] = logPath
-	output = logMatcher.MetadataIndex(input)
-
-	assert.Equal(t, output, cid)
+	assert.Equal(t, output, expectedResult)
 }