Alerting: Special alert instance if rule is in state NoData (#40540)

* do not suppress NoData state
* extract conversion of state to postable alert + tests
* create a special alert instance if nodata 
* use NoData when converting from Keep Last State instead of Alerting
* add silence during migration if NoData is mapped to KeepLastState.

pkg/services/ngalert/schedule/compat.go

@@ -8,13 +8,82 @@ import (
 
 	"github.com/go-openapi/strfmt"
 	"github.com/grafana/grafana-plugin-sdk-go/data"
-	apimodels "github.com/grafana/grafana/pkg/services/ngalert/api/tooling/definitions"
 	"github.com/prometheus/alertmanager/api/v2/models"
+	"github.com/prometheus/common/model"
 
+	apimodels "github.com/grafana/grafana/pkg/services/ngalert/api/tooling/definitions"
+	"github.com/grafana/grafana/pkg/services/ngalert/eval"
 	ngModels "github.com/grafana/grafana/pkg/services/ngalert/models"
 	"github.com/grafana/grafana/pkg/services/ngalert/state"
 )
 
+const (
+	NoDataAlertName = "DatasourceNoData"
+
+	Rulename = "rulename"
+)
+
+// stateToPostableAlert converts a state to a model that is accepted by Alertmanager. Annotations and Labels are copied from the state.
+// - if state has at least one result, a new label '__value_string__' is added to the label set
+// - the alert's GeneratorURL is constructed to point to the alert edit page
+// - if evaluation state is either NoData or Error, the resulting set of labels is changed:
+//   - original alert name (label: model.AlertNameLabel) is backed up to OriginalAlertName
+//   - label model.AlertNameLabel is overwritten to either NoDataAlertName or ErrorAlertName
+func stateToPostableAlert(alertState *state.State, appURL *url.URL) *models.PostableAlert {
+	nL := alertState.Labels.Copy()
+	nA := data.Labels(alertState.Annotations).Copy()
+
+	if len(alertState.Results) > 0 {
+		nA["__value_string__"] = alertState.Results[0].EvaluationString
+	}
+
+	var urlStr string
+	if uid := nL[ngModels.RuleUIDLabel]; len(uid) > 0 && appURL != nil {
+		u := *appURL
+		u.Path = path.Join(u.Path, fmt.Sprintf("/alerting/%s/edit", uid))
+		urlStr = u.String()
+	} else if appURL != nil {
+		urlStr = appURL.String()
+	} else {
+		urlStr = ""
+	}
+
+	if alertState.State == eval.NoData {
+		return noDataAlert(nL, nA, alertState, urlStr)
+	}
+
+	return &models.PostableAlert{
+		Annotations: models.LabelSet(nA),
+		StartsAt:    strfmt.DateTime(alertState.StartsAt),
+		EndsAt:      strfmt.DateTime(alertState.EndsAt),
+		Alert: models.Alert{
+			Labels:       models.LabelSet(nL),
+			GeneratorURL: strfmt.URI(urlStr),
+		},
+	}
+}
+
+// NoDataAlert is a special alert sent by Grafana to the Alertmanager, that indicates we received no data from the datasource.
+// It effectively replaces the legacy behavior of "Keep Last State" by separating the regular alerting flow from the no data scenario into a separate alerts.
+// The Alert is defined as:
+// {  alertname=DatasourceNoData rulename=original_alertname } + { rule labelset } + { rule annotations }
+func noDataAlert(labels data.Labels, annotations data.Labels, alertState *state.State, urlStr string) *models.PostableAlert {
+	if name, ok := labels[model.AlertNameLabel]; ok {
+		labels[Rulename] = name
+	}
+	labels[model.AlertNameLabel] = NoDataAlertName
+
+	return &models.PostableAlert{
+		Annotations: models.LabelSet(annotations),
+		StartsAt:    strfmt.DateTime(alertState.StartsAt),
+		EndsAt:      strfmt.DateTime(alertState.EndsAt),
+		Alert: models.Alert{
+			Labels:       models.LabelSet(labels),
+			GeneratorURL: strfmt.URI(urlStr),
+		},
+	}
+}
+
 func FromAlertStateToPostableAlerts(firingStates []*state.State, stateManager *state.Manager, appURL *url.URL) apimodels.PostableAlerts {
 	alerts := apimodels.PostableAlerts{PostableAlerts: make([]models.PostableAlert, 0, len(firingStates))}
 	var sentAlerts []*state.State
@@ -24,33 +93,8 @@ func FromAlertStateToPostableAlerts(firingStates []*state.State, stateManager *s
 		if !alertState.NeedsSending(stateManager.ResendDelay) {
 			continue
 		}
-		nL := alertState.Labels.Copy()
-		nA := data.Labels(alertState.Annotations).Copy()
-
-		if len(alertState.Results) > 0 {
-			nA["__value_string__"] = alertState.Results[0].EvaluationString
-		}
-
-		var urlStr string
-		if uid := nL[ngModels.RuleUIDLabel]; len(uid) > 0 && appURL != nil {
-			u := *appURL
-			u.Path = path.Join(u.Path, fmt.Sprintf("/alerting/%s/edit", uid))
-			urlStr = u.String()
-		} else if appURL != nil {
-			urlStr = appURL.String()
-		} else {
-			urlStr = ""
-		}
-
-		alerts.PostableAlerts = append(alerts.PostableAlerts, models.PostableAlert{
-			Annotations: models.LabelSet(nA),
-			StartsAt:    strfmt.DateTime(alertState.StartsAt),
-			EndsAt:      strfmt.DateTime(alertState.EndsAt),
-			Alert: models.Alert{
-				Labels:       models.LabelSet(nL),
-				GeneratorURL: strfmt.URI(urlStr),
-			},
-		})
+		alert := stateToPostableAlert(alertState, appURL)
+		alerts.PostableAlerts = append(alerts.PostableAlerts, *alert)
 		alertState.LastSentAt = ts
 		sentAlerts = append(sentAlerts, alertState)
 	}

pkg/services/ngalert/schedule/compat_test.go

@@ -0,0 +1,200 @@
+package schedule
+
+import (
+	"fmt"
+	"math/rand"
+	"net/url"
+	"testing"
+	"time"
+
+	"github.com/go-openapi/strfmt"
+	"github.com/prometheus/alertmanager/api/v2/models"
+	"github.com/prometheus/common/model"
+	"github.com/stretchr/testify/require"
+
+	"github.com/grafana/grafana/pkg/services/ngalert/eval"
+	ngModels "github.com/grafana/grafana/pkg/services/ngalert/models"
+	"github.com/grafana/grafana/pkg/services/ngalert/state"
+	"github.com/grafana/grafana/pkg/util"
+)
+
+func Test_stateToPostableAlert(t *testing.T) {
+	appURL := &url.URL{
+		Scheme: "http:",
+		Host:   fmt.Sprintf("host-%d", rand.Int()),
+		Path:   fmt.Sprintf("path-%d", rand.Int()),
+	}
+
+	testCases := []struct {
+		name  string
+		state eval.State
+	}{
+		{
+			name:  "when state is Normal",
+			state: eval.Normal,
+		},
+		{
+			name:  "when state is Alerting",
+			state: eval.Alerting,
+		},
+		{
+			name:  "when state is Pending",
+			state: eval.Pending,
+		},
+		{
+			name:  "when state is NoData",
+			state: eval.NoData,
+		},
+		{
+			name:  "when state is Error",
+			state: eval.Error,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Run("it generates proper URL", func(t *testing.T) {
+				t.Run("to alert rule", func(t *testing.T) {
+					alertState := randomState(tc.state)
+					alertState.Labels[ngModels.RuleUIDLabel] = alertState.AlertRuleUID
+					result := stateToPostableAlert(alertState, appURL)
+					u := *appURL
+					u.Path = u.Path + "/alerting/" + alertState.AlertRuleUID + "/edit"
+					require.Equal(t, u.String(), result.Alert.GeneratorURL.String())
+				})
+
+				t.Run("app URL as is if rule UID is not specified", func(t *testing.T) {
+					alertState := randomState(tc.state)
+					alertState.Labels[ngModels.RuleUIDLabel] = ""
+					result := stateToPostableAlert(alertState, appURL)
+					require.Equal(t, appURL.String(), result.Alert.GeneratorURL.String())
+
+					delete(alertState.Labels, ngModels.RuleUIDLabel)
+					result = stateToPostableAlert(alertState, appURL)
+					require.Equal(t, appURL.String(), result.Alert.GeneratorURL.String())
+				})
+
+				t.Run("empty string if app URL is not provided", func(t *testing.T) {
+					alertState := randomState(tc.state)
+					alertState.Labels[ngModels.RuleUIDLabel] = alertState.AlertRuleUID
+					result := stateToPostableAlert(alertState, nil)
+					require.Equal(t, "", result.Alert.GeneratorURL.String())
+				})
+			})
+
+			t.Run("Start and End timestamps should be the same", func(t *testing.T) {
+				alertState := randomState(tc.state)
+				result := stateToPostableAlert(alertState, appURL)
+				require.Equal(t, strfmt.DateTime(alertState.StartsAt), result.StartsAt)
+				require.Equal(t, strfmt.DateTime(alertState.EndsAt), result.EndsAt)
+			})
+
+			t.Run("should copy annotations", func(t *testing.T) {
+				alertState := randomState(tc.state)
+				alertState.Annotations = randomMapOfStrings()
+				result := stateToPostableAlert(alertState, appURL)
+				require.Equal(t, models.LabelSet(alertState.Annotations), result.Annotations)
+
+				t.Run("add __value_string__ if it has results", func(t *testing.T) {
+					alertState := randomState(tc.state)
+					alertState.Annotations = randomMapOfStrings()
+					expectedValueString := util.GenerateShortUID()
+					alertState.Results = []state.Evaluation{
+						{
+							EvaluationString: expectedValueString,
+						},
+					}
+
+					result := stateToPostableAlert(alertState, appURL)
+
+					expected := make(models.LabelSet, len(alertState.Annotations)+1)
+					for k, v := range alertState.Annotations {
+						expected[k] = v
+					}
+					expected["__value_string__"] = expectedValueString
+
+					require.Equal(t, expected, result.Annotations)
+
+					// even overwrites
+					alertState.Annotations["__value_string__"] = util.GenerateShortUID()
+					result = stateToPostableAlert(alertState, appURL)
+					require.Equal(t, expected, result.Annotations)
+				})
+			})
+
+			switch tc.state {
+			case eval.NoData:
+				t.Run("should keep existing labels and change name", func(t *testing.T) {
+					alertState := randomState(tc.state)
+					alertState.Labels = randomMapOfStrings()
+					alertName := util.GenerateShortUID()
+					alertState.Labels[model.AlertNameLabel] = alertName
+
+					result := stateToPostableAlert(alertState, appURL)
+
+					expected := make(models.LabelSet, len(alertState.Labels)+1)
+					for k, v := range alertState.Labels {
+						expected[k] = v
+					}
+					expected[model.AlertNameLabel] = NoDataAlertName
+					expected[Rulename] = alertName
+
+					require.Equal(t, expected, result.Labels)
+
+					t.Run("should not backup original alert name if it does not exist", func(t *testing.T) {
+						alertState := randomState(tc.state)
+						alertState.Labels = randomMapOfStrings()
+						delete(alertState.Labels, model.AlertNameLabel)
+
+						result := stateToPostableAlert(alertState, appURL)
+
+						require.Equal(t, NoDataAlertName, result.Labels[model.AlertNameLabel])
+						require.NotContains(t, result.Labels[model.AlertNameLabel], Rulename)
+					})
+				})
+			default:
+				t.Run("should copy labels as is", func(t *testing.T) {
+					alertState := randomState(tc.state)
+					alertState.Labels = randomMapOfStrings()
+					result := stateToPostableAlert(alertState, appURL)
+					require.Equal(t, models.LabelSet(alertState.Labels), result.Labels)
+				})
+			}
+		})
+	}
+}
+
+func randomMapOfStrings() map[string]string {
+	max := 5
+	result := make(map[string]string, max)
+	for i := 0; i < max; i++ {
+		result[util.GenerateShortUID()] = util.GenerateShortUID()
+	}
+	return result
+}
+
+func randomDuration() time.Duration {
+	return time.Duration(rand.Int63n(599)+1) * time.Second
+}
+
+func randomTimeInFuture() time.Time {
+	return time.Now().Add(randomDuration())
+}
+
+func randomTimeInPast() time.Time {
+	return time.Now().Add(-randomDuration())
+}
+
+func randomState(evalState eval.State) *state.State {
+	return &state.State{
+		State:              evalState,
+		AlertRuleUID:       util.GenerateShortUID(),
+		StartsAt:           time.Now(),
+		EndsAt:             randomTimeInFuture(),
+		LastEvaluationTime: randomTimeInPast(),
+		EvaluationDuration: randomDuration(),
+		LastSentAt:         randomTimeInPast(),
+		Annotations:        make(map[string]string),
+		Labels:             make(map[string]string),
+	}
+}

pkg/services/ngalert/state/state.go

@@ -4,6 +4,7 @@ import (
 	"time"
 
 	"github.com/grafana/grafana-plugin-sdk-go/data"
+
 	"github.com/grafana/grafana/pkg/services/ngalert/eval"
 	ngModels "github.com/grafana/grafana/pkg/services/ngalert/models"
 )
@@ -113,16 +114,12 @@ func (a *State) resultNoData(alertRule *ngModels.AlertRule, result eval.Result)
 }
 
 func (a *State) NeedsSending(resendDelay time.Duration) bool {
-	if a.State != eval.Alerting && a.State != eval.Normal {
-		return false
-	}
-
-	if a.State == eval.Normal && !a.Resolved {
+	if a.State == eval.Pending || a.State == eval.Error || a.State == eval.Normal && !a.Resolved {
 		return false
 	}
 	// if LastSentAt is before or equal to LastEvaluationTime + resendDelay, send again
-	return a.LastSentAt.Add(resendDelay).Before(a.LastEvaluationTime) ||
-		a.LastSentAt.Add(resendDelay).Equal(a.LastEvaluationTime)
+	nextSent := a.LastSentAt.Add(resendDelay)
+	return nextSent.Before(a.LastEvaluationTime) || nextSent.Equal(a.LastEvaluationTime)
 }
 
 func (a *State) Equals(b *State) bool {

pkg/services/ngalert/state/state_test.go

@@ -1,6 +1,7 @@
 package state
 
 import (
+	"math/rand"
 	"testing"
 	"time"
 
@@ -99,6 +100,46 @@ func TestNeedsSending(t *testing.T) {
 				LastSentAt:         evaluationTime.Add(-1 * time.Minute),
 			},
 		},
+		{
+			name:        "state: no-data, needs to be re-sent",
+			expected:    true,
+			resendDelay: 1 * time.Minute,
+			testState: &State{
+				State:              eval.NoData,
+				LastEvaluationTime: evaluationTime,
+				LastSentAt:         evaluationTime.Add(-1 * time.Minute),
+			},
+		},
+		{
+			name:        "state: no-data, should not be re-sent",
+			expected:    false,
+			resendDelay: 1 * time.Minute,
+			testState: &State{
+				State:              eval.NoData,
+				LastEvaluationTime: evaluationTime,
+				LastSentAt:         evaluationTime.Add(-time.Duration(rand.Int63n(59)+1) * time.Second),
+			},
+		},
+		{
+			name:        "state: error, needs to be re-sent",
+			expected:    false,
+			resendDelay: 1 * time.Minute,
+			testState: &State{
+				State:              eval.Error,
+				LastEvaluationTime: evaluationTime,
+				LastSentAt:         evaluationTime.Add(-1 * time.Minute),
+			},
+		},
+		{
+			name:        "state: error, should not be re-sent",
+			expected:    false,
+			resendDelay: 1 * time.Minute,
+			testState: &State{
+				State:              eval.Error,
+				LastEvaluationTime: evaluationTime,
+				LastSentAt:         evaluationTime.Add(-time.Duration(rand.Int63n(59)+1) * time.Second),
+			},
+		},
 	}
 
 	for _, tc := range testCases {

pkg/services/sqlstore/migrations/ualert/alert_rule.go

@@ -131,6 +131,10 @@ func (m *migration) makeAlertRule(cond condition, da dashAlert, folderUID string
 		m.mg.Logger.Error("alert migration error: failed to create silence", "rule_name", ar.Title, "err", err)
 	}
 
+	if err := m.addNoDataSilence(da, ar); err != nil {
+		m.mg.Logger.Error("alert migration error: failed to create silence for NoData", "rule_name", ar.Title, "err", err)
+	}
+
 	return ar, nil
 }
 
@@ -201,7 +205,7 @@ func transNoData(s string) (string, error) {
 	case "alerting":
 		return "Alerting", nil
 	case "keep_state":
-		return "Alerting", nil
+		return "NoData", nil // "keep last state" translates to no data because we now emit a special alert when the state is "noData". The result is that the evaluation will not return firing and instead we'll raise the special alert.
 	}
 	return "", fmt.Errorf("unrecognized No Data setting %v", s)
 }

pkg/services/sqlstore/migrations/ualert/silences.go

@@ -14,10 +14,16 @@ import (
 	"github.com/gofrs/uuid"
 	"github.com/matttproud/golang_protobuf_extensions/pbutil"
 	pb "github.com/prometheus/alertmanager/silence/silencepb"
+	"github.com/prometheus/common/model"
 
 	"github.com/grafana/grafana/pkg/services/sqlstore/migrator"
 )
 
+const (
+	// Should be the same as 'NoDataAlertName' in pkg/services/schedule/compat.go.
+	NoDataAlertName = "DatasourceNoData"
+)
+
 func (m *migration) addSilence(da dashAlert, rule *alertRule) error {
 	if da.State != "paused" {
 		return nil
@@ -55,6 +61,46 @@ func (m *migration) addSilence(da dashAlert, rule *alertRule) error {
 	return nil
 }
 
+func (m *migration) addNoDataSilence(da dashAlert, rule *alertRule) error {
+	if da.ParsedSettings.NoDataState != "keep_state" {
+		return nil
+	}
+
+	uid, err := uuid.NewV4()
+	if err != nil {
+		return errors.New("failed to create uuid for silence")
+	}
+
+	s := &pb.MeshSilence{
+		Silence: &pb.Silence{
+			Id: uid.String(),
+			Matchers: []*pb.Matcher{
+				{
+					Type:    pb.Matcher_EQUAL,
+					Name:    model.AlertNameLabel,
+					Pattern: NoDataAlertName,
+				},
+				{
+					Type:    pb.Matcher_EQUAL,
+					Name:    "rule_uid",
+					Pattern: rule.UID,
+				},
+			},
+			StartsAt:  time.Now(),
+			EndsAt:    time.Now().AddDate(1, 0, 0), // 1 year.
+			CreatedBy: "Grafana Migration",
+			Comment:   fmt.Sprintf("Created during migration to unified alerting to silence NoData state for alert rule ID '%s' and Title '%s' because the option 'Keep Last State' was selected for NoData state", rule.UID, rule.Title),
+		},
+		ExpiresAt: time.Now().AddDate(1, 0, 0), // 1 year.
+	}
+	_, ok := m.silences[da.OrgId]
+	if !ok {
+		m.silences[da.OrgId] = make([]*pb.MeshSilence, 0)
+	}
+	m.silences[da.OrgId] = append(m.silences[da.OrgId], s)
+	return nil
+}
+
 func (m *migration) writeSilencesFile(orgID int64) error {
 	var buf bytes.Buffer
 	orgSilences, ok := m.silences[orgID]