monitoring: Add OpenMetrics exporter

This patch makes chasquid's monitoring server expose an OpenMetrics metrics endpoint. It adds a new package "expvarom" which implements an HTTP handler that exports expvar variables in the OpenMetrics text format. Then, the handler is registered by the monitoring server at /metrics (where most things expect it to be). The existing exported variables are also extended with descriptions, which is optional, but improves the readability of the metrics.
2025-12-20 15:07:03 +00:00 · 2020-08-19 20:42:28 +01:00
parent 7e412db19b
commit 7fe42a368a
12 changed files with 447 additions and 154 deletions
--- a/internal/expvarom/expvarom_test.go
+++ b/internal/expvarom/expvarom_test.go
@@ -0,0 +1,127 @@
+package expvarom
+
+import (
+	"expvar"
+	"io/ioutil"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+var (
+	testI1 = NewInt("testI1", "int test var")
+	testI2 = expvar.NewInt("testI2")
+
+	testF = NewFloat("testF", "float test var")
+
+	testMI  = NewMap("testMI", "label", "int map test var")
+	testMF  = NewMap("testMF", "label", "float map test var")
+	testMXI = expvar.NewMap("testMXI")
+	testMXF = expvar.NewMap("testMXF")
+
+	testMEmpty = expvar.NewMap("testMEmpty") //nolint // Unused.
+
+	testMOther = expvar.NewMap("testMOther")
+
+	testS = expvar.NewString("testS")
+
+	// Naming test cases.
+	testN1 = expvar.NewInt("name/1z")
+	testN2 = NewInt("name$2", "name with $")
+	testN3 = expvar.NewInt("3name")
+	testN4 = expvar.NewInt("nAme_4Z")
+	testN5 = expvar.NewInt("ñame_5")
+)
+
+const expected string = `_ame_5 5
+
+i3name 3
+
+nAme_4Z 4
+
+name_1z 1
+
+# HELP name_2 name with $
+name_2 2
+
+# HELP testF float test var
+testF 3.43434
+
+# HELP testI1 int test var
+testI1 1
+
+testI2 2
+
+# HELP testMF float map test var
+testMF{label="key2.0"} 6.6
+testMF{label="key2.1"} 6.61
+testMF{label="key2.2-ñaca"} 6.62
+testMF{label="key2.3-a\\b"} 6.63
+testMF{label="key2.4-	"} 6.64
+testMF{label="key2.5-a\nb"} 6.65
+testMF{label="key2.6-a\"b"} 6.66
+testMF{label="key2.7-\\u00f1aca-A\\t\\xff\\xfe\\xfdB"} 6.67
+
+# HELP testMI int map test var
+testMI{label="key1"} 5
+
+testMXF{key="key4"} 8e-08
+
+testMXI{key="key3"} 7
+
+# Generated by expvarom
+# EXPERIMENTAL - Format is not fully standard yet
+# Ignored variables: ["cmdline" "memstats" "testS"]
+`
+
+func TestHandler(t *testing.T) {
+	testI1.Add(1)
+	testI2.Add(2)
+	testF.Add(3.43434)
+	testMI.Add("key1", 5)
+
+	// Test some strange keys in this map to check they're escaped properly.
+	testMF.AddFloat("key2.0", 6.60)
+	testMF.AddFloat("key2.1", 6.61)
+	testMF.AddFloat("key2.2-ñaca", 6.62)
+	testMF.AddFloat(`key2.3-a\b`, 6.63)
+	testMF.AddFloat("key2.4-\t", 6.64)
+	testMF.AddFloat("key2.5-a\nb", 6.65)
+	testMF.AddFloat(`key2.6-a"b`, 6.66)
+	testMF.AddFloat("key2.7-ñaca-A\t\xff\xfe\xfdB", 6.67) // Invalid utf8.
+
+	testMXI.Add("key3", 7)
+	testMXF.AddFloat("key4", 8e-8)
+	testS.Set("lalala")
+
+	testN1.Add(1)
+	testN2.Add(2)
+	testN3.Add(3)
+	testN4.Add(4)
+	testN5.Add(5)
+
+	// Map with an unsupported type.
+	testMOther.Set("keyX", &expvar.String{})
+
+	req := httptest.NewRequest("get", "/metrics", nil)
+	w := httptest.NewRecorder()
+	MetricsHandler(w, req)
+
+	resp := w.Result()
+	body, _ := ioutil.ReadAll(resp.Body)
+
+	if diff := cmp.Diff(expected, string(body)); diff != "" {
+		t.Errorf("MetricsHandler() mismatch (-want +got):\n%s", diff)
+	}
+}
+
+func TestMapLabelAccident(t *testing.T) {
+	defer func() {
+		if r := recover(); r == nil {
+			t.Errorf("NewMap did not panic as expected")
+		}
+	}()
+
+	NewMap("name", "label with spaces", "description")
+}