Alertmanager: Add ExtraData field to experimental pre-notification hook (#12481)

#### What this PR does
Adds another field `ExtraData` to `hookData` which is a
`json.RawMessage` - this additional data is then passed along via the
context.

#### Checklist

- [x] Tests updated.
- [x] Documentation added.
- [x] `CHANGELOG.md` updated - the order of entries should be
`[CHANGE]`, `[FEATURE]`, `[ENHANCEMENT]`, `[BUGFIX]`. If changelog entry
is not needed, please add the `changelog-not-needed` label to the PR.
- [x]
[`about-versioning.md`](https://github.com/grafana/mimir/blob/main/docs/sources/mimir/configure/about-versioning.md)
updated with experimental features.

Author: fayzal-g

pkg/alertmanager/notify_hooks_notifier.go

@@ -105,12 +105,15 @@ func newNotifyHooksMetrics(reg prometheus.Registerer) *notifyHooksMetrics {
 }
 
 func (n *notifyHooksNotifier) Notify(ctx context.Context, alerts ...*types.Alert) (bool, error) {
-	newAlerts := n.apply(ctx, alerts)
+	result := n.apply(ctx, alerts)
 
-	return n.upstream.Notify(ctx, newAlerts...)
+	// Add additional data from pre-notify hook to the context
+	ctxWithData := withExtraData(ctx, result.ExtraData)
+
+	return n.upstream.Notify(ctxWithData, result.Alerts...)
 }
 
-func (n *notifyHooksNotifier) apply(ctx context.Context, alerts []*types.Alert) []*types.Alert {
+func (n *notifyHooksNotifier) apply(ctx context.Context, alerts []*types.Alert) *hookData {
 	l := n.logger
 
 	receiver, _ := notify.ReceiverName(ctx)
@@ -122,19 +125,23 @@ func (n *notifyHooksNotifier) apply(ctx context.Context, alerts []*types.Alert)
 	url := n.limits.AlertmanagerNotifyHookURL(n.user)
 	if url == "" {
 		level.Debug(l).Log("msg", "Notify hooks not applied, no URL configured")
-		return alerts
+		return &hookData{
+			Alerts: alerts,
+		}
 	}
 
 	receivers := n.limits.AlertmanagerNotifyHookReceivers(n.user)
 	if len(receivers) > 0 && !slices.Contains(receivers, receiver) {
 		level.Debug(l).Log("msg", "Notify hooks not applied, not enabled for receiver")
-		return alerts
+		return &hookData{
+			Alerts: alerts,
+		}
 	}
 
 	timeout := n.limits.AlertmanagerNotifyHookTimeout(n.user)
 
 	start := time.Now()
-	newAlerts, code, err := n.invoke(ctx, l, url, timeout, alerts)
+	result, code, err := n.invoke(ctx, l, url, timeout, alerts)
 
 	duration := time.Since(start)
 	n.metrics.hookDuration.Observe(float64(duration))
@@ -156,12 +163,14 @@ func (n *notifyHooksNotifier) apply(ctx context.Context, alerts []*types.Alert)
 			n.metrics.hookFailed.WithLabelValues(status).Inc()
 			level.Error(l).Log("msg", "Notify hooks failed", "err", err)
 		}
-		return alerts
+		return &hookData{
+			Alerts: alerts,
+		}
 	}
 
 	level.Debug(l).Log("msg", "Notify hooks applied successfully")
 
-	return newAlerts
+	return result
 }
 
 // hookData is the payload we send and receive from the notification hook.
@@ -170,6 +179,18 @@ type hookData struct {
 	Status      string         `json:"status"`
 	Alerts      []*types.Alert `json:"alerts"`
 	GroupLabels model.LabelSet `json:"groupLabels"`
+
+	ExtraData json.RawMessage `json:"extraData,omitempty"`
+}
+
+type extraDataKey int
+
+const (
+	ExtraDataKey extraDataKey = iota
+)
+
+func withExtraData(ctx context.Context, extraData json.RawMessage) context.Context {
+	return context.WithValue(ctx, ExtraDataKey, extraData)
 }
 
 func (n *notifyHooksNotifier) getData(ctx context.Context, l log.Logger, alerts []*types.Alert) *hookData {
@@ -190,7 +211,7 @@ func (n *notifyHooksNotifier) getData(ctx context.Context, l log.Logger, alerts
 	}
 }
 
-func (n *notifyHooksNotifier) invoke(ctx context.Context, l log.Logger, url string, timeout time.Duration, alerts []*types.Alert) ([]*types.Alert, int, error) {
+func (n *notifyHooksNotifier) invoke(ctx context.Context, l log.Logger, url string, timeout time.Duration, alerts []*types.Alert) (*hookData, int, error) {
 	logger, ctx := spanlogger.New(ctx, l, tracer, "NotifyHooksNotifier.Invoke")
 	defer logger.Finish()
 
@@ -240,5 +261,5 @@ func (n *notifyHooksNotifier) invoke(ctx context.Context, l log.Logger, url stri
 		return nil, 0, err
 	}
 
-	return result.Alerts, 0, nil
+	return &result, 0, nil
 }

pkg/alertmanager/notify_hooks_notifier_test.go

@@ -4,6 +4,7 @@ package alertmanager
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"io"
 	"net/http"
@@ -24,10 +25,12 @@ import (
 )
 
 type fakeNotifier struct {
-	calls [][]*types.Alert
+	ctxForTesting context.Context
+	calls         [][]*types.Alert
 }
 
-func (m *fakeNotifier) Notify(_ context.Context, alerts ...*types.Alert) (bool, error) {
+func (m *fakeNotifier) Notify(ctx context.Context, alerts ...*types.Alert) (bool, error) {
+	m.ctxForTesting = ctx
 	m.calls = append(m.calls, alerts)
 	return false, nil
 }
@@ -182,7 +185,9 @@ func TestNotifyHooksNotifier(t *testing.T) {
 		`"endsAt":"0001-01-01T00:00:00Z",` +
 		`"generatorURL":"",` +
 		`"UpdatedAt":"0001-01-01T00:00:00Z",` +
-		`"Timeout":false}]}`
+		`"Timeout":false}],` +
+		`"extraData": {"foo": "bar"}` +
+		`}`
 
 	t.Run("hook invoked", func(t *testing.T) {
 		f := newTestHooksFixture(t, http.StatusOK, okResponse)
@@ -193,6 +198,24 @@ func TestNotifyHooksNotifier(t *testing.T) {
 		require.Equal(t, [][]*types.Alert{makeAlert("changed")}, f.upstream.calls)
 		f.assertMetricsSuccess(t, 1, 0)
 	})
+	t.Run("hook invoked with extra data", func(t *testing.T) {
+		f := newTestHooksFixture(t, http.StatusOK, okResponse)
+		ctx := makeContext()
+
+		_, err := f.notifier.Notify(ctx, makeAlert("foo")...)
+		require.NoError(t, err)
+
+		type testExtraData struct {
+			Foo string `json:"foo"`
+		}
+
+		extraDataRaw := f.upstream.ctxForTesting.Value(ExtraDataKey).(json.RawMessage)
+		extraData := testExtraData{}
+		err = json.Unmarshal(extraDataRaw, &extraData)
+		require.NoError(t, err)
+
+		require.Equal(t, "bar", extraData.Foo)
+	})
 	t.Run("hook not invoked when empty url configured", func(t *testing.T) {
 		f := newTestHooksFixture(t, http.StatusOK, okResponse)
 		f.limits.url = ""