From 95d8cf04d8ff731a5c71a97006925fbab560941e Mon Sep 17 00:00:00 2001
From: harpunius <harpunius@gmail.com>
Date: Tue, 8 Oct 2024 15:06:14 +0200
Subject: [PATCH] fix(prometheus_sink): log errors and fallback to default
 metric mapper

Signed-off-by: harpunius <harpunius@gmail.com>
---
 src/stats/prom/prometheus_sink.go      | 22 ++++++++++++++++++----
 src/stats/prom/prometheus_sink_test.go | 25 +++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/src/stats/prom/prometheus_sink.go b/src/stats/prom/prometheus_sink.go
index 58b27ece..b0fbb328 100644
--- a/src/stats/prom/prometheus_sink.go
+++ b/src/stats/prom/prometheus_sink.go
@@ -116,10 +116,24 @@ func NewPrometheusSink(opts ...prometheusSinkOption) gostats.Sink {
 		logrus.Infof("Starting prometheus sink on %s%s", sink.config.addr, sink.config.path)
 		_ = http.ListenAndServe(sink.config.addr, nil)
 	}()
-	if sink.config.mapperYamlPath != "" {
-		_ = sink.mapper.InitFromFile(sink.config.mapperYamlPath)
-	} else {
-		_ = sink.mapper.InitFromYAMLString(defaultMapper)
+
+	useDefaultMapper := sink.config.mapperYamlPath == ""
+	if !useDefaultMapper {
+		err := sink.mapper.InitFromFile(sink.config.mapperYamlPath)
+		if err != nil {
+			logrus.Errorf("Failed parsing metric mapper from path %s", sink.config.mapperYamlPath)
+
+			// Fallback to using the default mapper
+			useDefaultMapper = true
+		}
+	}
+
+	if useDefaultMapper {
+		logrus.Infof("Using default metric mapper")
+		err := sink.mapper.InitFromYAMLString(defaultMapper)
+		if err != nil {
+			logrus.Error("Failed parsing default metric mapper")
+		}
 	}
 
 	sink.exp = exporter.NewExporter(promRegistry,
diff --git a/src/stats/prom/prometheus_sink_test.go b/src/stats/prom/prometheus_sink_test.go
index cc4b8900..9786cc20 100644
--- a/src/stats/prom/prometheus_sink_test.go
+++ b/src/stats/prom/prometheus_sink_test.go
@@ -109,3 +109,28 @@ func TestFlushTimer(t *testing.T) {
 		return true
 	}, time.Second, time.Millisecond)
 }
+
+func TestPrometheusSinkMetricMapperDefaultHandling(t *testing.T) {
+	// Pass a metric mapper that doesn't exist
+	s := NewPrometheusSink(WithMapperYamlPath("file_not_found.yaml"), WithPath("/otherMetrics"))
+
+	s.FlushTimer("ratelimit.service.rate_limit.rds.database_users.within_limit", 1)
+	assert.Eventually(t, func() bool {
+		metricFamilies, err := prometheus.DefaultGatherer.Gather()
+		require.NoError(t, err)
+
+		metrics := make(map[string]*dto.MetricFamily)
+		for _, metricFamily := range metricFamilies {
+			metrics[*metricFamily.Name] = metricFamily
+		}
+
+		m, ok := metrics["ratelimit_service_rate_limit_within_limit"]
+		require.True(t, ok)
+		require.Len(t, m.Metric, 1)
+		require.Equal(t, map[string]string{
+			"domain": "rds",
+			"key1":   "database_users",
+		}, toMap(m.Metric[0].Label))
+		return true
+	}, time.Second, time.Millisecond)
+}