[Alerting] Route validations (#34393)

* more routing validation

* go mod

* recursive route validations

go.mod

@@ -14,7 +14,7 @@ replace k8s.io/client-go => k8s.io/client-go v0.18.8
 require (
 	cloud.google.com/go/storage v1.14.0
 	cuelang.org/go v0.3.2
-	github.com/Azure/azure-sdk-for-go/sdk/azcore v0.16.0 // indirect
+	github.com/Azure/azure-sdk-for-go/sdk/azcore v0.16.0
 	github.com/Azure/azure-sdk-for-go/sdk/azidentity v0.8.0
 	github.com/BurntSushi/toml v0.3.1
 	github.com/Masterminds/semver v1.5.0

pkg/services/ngalert/api/tooling/definitions/alertmanager.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"reflect"
 
+	"github.com/pkg/errors"
 	amv2 "github.com/prometheus/alertmanager/api/v2/models"
 	"github.com/prometheus/alertmanager/config"
 	"gopkg.in/yaml.v3"
@@ -484,10 +485,26 @@ func (c *Config) UnmarshalJSON(b []byte) error {
 		}
 	}
 
-	if c.Route != nil {
-		if err := c.Route.UnmarshalYAML(noopUnmarshal); err != nil {
-			return err
-		}
+	if c.Route == nil {
+		return fmt.Errorf("no routes provided")
+	}
+
+	// Route is a recursive structure that includes validation in the yaml unmarshaler.
+	// Therefore, we'll redirect json -> yaml to utilize these.
+	b, err := yaml.Marshal(c.Route)
+	if err != nil {
+		return errors.Wrap(err, "marshaling route to yaml for validation")
+	}
+	err = yaml.Unmarshal(b, c.Route)
+	if err != nil {
+		return errors.Wrap(err, "unmarshaling route for validations")
+	}
+
+	if len(c.Route.Receiver) == 0 {
+		return fmt.Errorf("root route must specify a default receiver")
+	}
+	if len(c.Route.Match) > 0 || len(c.Route.MatchRE) > 0 {
+		return fmt.Errorf("root route must not have any matchers")
 	}
 
 	for _, r := range c.InhibitRules {

pkg/services/ngalert/api/tooling/definitions/alertmanager_test.go

@@ -243,6 +243,101 @@ func Test_ApiAlertingConfig_Marshaling(t *testing.T) {
 			},
 			err: true,
 		},
+		{
+			desc: "failure graf no route",
+			input: PostableApiAlertingConfig{
+				Receivers: []*PostableApiReceiver{
+					{
+						Receiver: config.Receiver{
+							Name: "graf",
+						},
+						PostableGrafanaReceivers: PostableGrafanaReceivers{
+							GrafanaManagedReceivers: []*PostableGrafanaReceiver{{}},
+						},
+					},
+				},
+			},
+			err: true,
+		},
+		{
+			desc: "failure graf no default receiver",
+			input: PostableApiAlertingConfig{
+				Config: Config{
+					Route: &config.Route{
+						Routes: []*config.Route{
+							{
+								Receiver: "graf",
+							},
+						},
+					},
+				},
+				Receivers: []*PostableApiReceiver{
+					{
+						Receiver: config.Receiver{
+							Name: "graf",
+						},
+						PostableGrafanaReceivers: PostableGrafanaReceivers{
+							GrafanaManagedReceivers: []*PostableGrafanaReceiver{{}},
+						},
+					},
+				},
+			},
+			err: true,
+		},
+		{
+			desc: "failure graf root route with matchers",
+			input: PostableApiAlertingConfig{
+				Config: Config{
+					Route: &config.Route{
+						Receiver: "graf",
+						Routes: []*config.Route{
+							{
+								Receiver: "graf",
+							},
+						},
+						Match: map[string]string{"foo": "bar"},
+					},
+				},
+				Receivers: []*PostableApiReceiver{
+					{
+						Receiver: config.Receiver{
+							Name: "graf",
+						},
+						PostableGrafanaReceivers: PostableGrafanaReceivers{
+							GrafanaManagedReceivers: []*PostableGrafanaReceiver{{}},
+						},
+					},
+				},
+			},
+			err: true,
+		},
+		{
+			desc: "failure graf nested route duplicate group by labels",
+			input: PostableApiAlertingConfig{
+				Config: Config{
+					Route: &config.Route{
+						Receiver: "graf",
+						Routes: []*config.Route{
+							{
+								Receiver:   "graf",
+								GroupByStr: []string{"foo", "bar", "foo"},
+							},
+						},
+					},
+				},
+				Receivers: []*PostableApiReceiver{
+					{
+						Receiver: config.Receiver{
+							Name: "graf",
+						},
+						PostableGrafanaReceivers: PostableGrafanaReceivers{
+							GrafanaManagedReceivers: []*PostableGrafanaReceiver{{}},
+						},
+					},
+				},
+			},
+			err: true,
+		},
 	} {
 		t.Run(tc.desc, func(t *testing.T) {
 			encoded, err := json.Marshal(tc.input)