feat: Adds 'cq' diagnostics to /debug/vars (#26874)

This PR adds continuous query diags to our /debug/vars endpoint

Example
```
  "cq": {
    "queryFail": 0,
    "queryOk": 2
  },
```

cmd/influxd/run/server.go

@@ -416,6 +416,9 @@ func (s *Server) appendContinuousQueryService(c continuous_querier.Config) {
 	srv.QueryExecutor = s.QueryExecutor
 	srv.Monitor = s.Monitor
 	s.Services = append(s.Services, srv)
+	if s.Monitor != nil {
+		s.Monitor.RegisterDiagnosticsClient("cq", srv)
+	}
 }
 
 // Err returns an error channel that multiplexes all out of band errors received from all services.

monitor/service.go

@@ -241,6 +241,7 @@ func (m *Monitor) Close() error {
 	m.DeregisterDiagnosticsClient("system")
 	m.DeregisterDiagnosticsClient("stats")
 	m.DeregisterDiagnosticsClient("config")
+	m.DeregisterDiagnosticsClient("cq")
 	return nil
 }
 

monitor/service_test.go

@@ -13,9 +13,11 @@ import (
 
 	"github.com/influxdata/influxdb/models"
 	"github.com/influxdata/influxdb/monitor"
+	"github.com/influxdata/influxdb/services/continuous_querier"
 	"github.com/influxdata/influxdb/services/meta"
 	"github.com/influxdata/influxdb/toml"
 	"github.com/influxdata/influxdb/tsdb"
+	"github.com/stretchr/testify/require"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zaptest/observer"
 )
@@ -414,6 +416,26 @@ func TestMonitor_QuickClose(t *testing.T) {
 	}
 }
 
+func TestMonitor_CQStatistics(t *testing.T) {
+	s := monitor.New(nil, monitor.Config{}, &tsdb.Config{})
+	err := s.Open()
+	require.NoError(t, err, "monitor open")
+	defer s.Close()
+
+	s.RegisterDiagnosticsClient("cq", continuous_querier.NewService(continuous_querier.NewConfig()))
+	stats, err := s.Statistics(nil)
+	require.NoError(t, err, "cq statistics")
+
+	for _, stat := range stats {
+		if stat.Name == "cq" {
+			require.Equal(t, stat.Values, map[string]interface{}{
+				"queryOk":   0,
+				"queryFail": 0,
+			}, "statistics")
+		}
+	}
+}
+
 func TestStatistic_ValueNames(t *testing.T) {
 	statistic := monitor.Statistic{
 		Statistic: models.Statistic{

services/continuous_querier/service.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/influxdata/influxdb/logger"
 	"github.com/influxdata/influxdb/models"
+	"github.com/influxdata/influxdb/monitor/diagnostics"
 	"github.com/influxdata/influxdb/query"
 	"github.com/influxdata/influxdb/services/meta"
 	"github.com/influxdata/influxql"
@@ -169,6 +170,12 @@ func (s *Service) Statistics(tags map[string]string) []models.Statistic {
 	}}
 }
 
+// Required for Monitor interface. Currently does not return any
+// diagnostic values.
+func (s *Service) Diagnostics() (*diagnostics.Diagnostics, error) {
+	return &diagnostics.Diagnostics{}, nil
+}
+
 // Run runs the specified continuous query, or all CQs if none is specified.
 func (s *Service) Run(database, name string, t time.Time) error {
 	var dbs []meta.DatabaseInfo

services/httpd/handler.go

@@ -2395,6 +2395,33 @@ func (h *Handler) serveExpvar(w http.ResponseWriter, r *http.Request) {
 	uniqueKeys := make(map[string]int)
 
 	for _, s := range stats {
+		if s.Name == "cq" {
+			jv, err := parseCQStatistics(&s.Statistic)
+			if err != nil {
+				h.httpError(w, err.Error(), http.StatusInternalServerError)
+				return
+			}
+			data, err := json.Marshal(jv)
+			if err != nil {
+				h.httpError(w, err.Error(), http.StatusInternalServerError)
+				return
+			}
+
+			if !first {
+				_, err := fmt.Fprintln(w, ",")
+				if err != nil {
+					h.httpError(w, err.Error(), http.StatusInternalServerError)
+					return
+				}
+			}
+			first = false
+			_, err = fmt.Fprintf(w, "\"cq\": %s", data)
+			if err != nil {
+				h.httpError(w, err.Error(), http.StatusInternalServerError)
+				return
+			}
+			continue
+		}
 		val, err := json.Marshal(s)
 		if err != nil {
 			continue
@@ -2644,6 +2671,14 @@ func parseConfigDiagnostics(d *diagnostics.Diagnostics) (map[string]interface{},
 	return m, nil
 }
 
+func parseCQStatistics(s *models.Statistic) (map[string]interface{}, error) {
+	if len(s.Values) == 0 {
+		return nil, fmt.Errorf("no cq statistics data available")
+	}
+
+	return s.Values, nil
+}
+
 // httpError writes an error to the client in a standard format.
 func (h *Handler) httpError(w http.ResponseWriter, errmsg string, code int) {
 	if code == http.StatusUnauthorized {