Alerting: Add support for retrieving imported Prometheus Alertmanager configurations (#106864)

pkg/services/ngalert/api/api_convert_prometheus.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -10,6 +11,8 @@ import (
 	"strings"
 	"time"
 
+	amconfig "github.com/prometheus/alertmanager/config"
+	"github.com/prometheus/alertmanager/pkg/labels"
 	prommodel "github.com/prometheus/common/model"
 	"gopkg.in/yaml.v3"
 
@@ -47,6 +50,13 @@ const (
 	// notificationSettingsHeader is the header that specifies the notification settings to be used for the rules.
 	// The value should be a JSON-encoded AlertRuleNotificationSettings object.
 	notificationSettingsHeader = "X-Grafana-Alerting-Notification-Settings"
+
+	// mergeMatchersHeader is the header that specifies the merge matchers for imported Alertmanager config.
+	// The value should be comma-separated key=value pairs, e.g., "environment=production,team=alerting".
+	mergeMatchersHeader = "X-Grafana-Alerting-Merge-Matchers"
+
+	// configIdentifierHeader is the header that specifies the identifier for imported Alertmanager config.
+	configIdentifierHeader = "X-Grafana-Alerting-Config-Identifier"
 )
 
 var (
@@ -113,6 +123,11 @@ type ConvertPrometheusSrv struct {
 	datasourceCache  datasources.CacheService
 	alertRuleService *provisioning.AlertRuleService
 	featureToggles   featuremgmt.FeatureToggles
+	am               Alertmanager
+}
+
+type Alertmanager interface {
+	GetAlertmanagerConfiguration(ctx context.Context, org int64, withAutogen bool) (apimodels.GettableUserConfig, error)
 }
 
 func NewConvertPrometheusSrv(
@@ -122,6 +137,7 @@ func NewConvertPrometheusSrv(
 	datasourceCache datasources.CacheService,
 	alertRuleService *provisioning.AlertRuleService,
 	featureToggles featuremgmt.FeatureToggles,
+	am Alertmanager,
 ) *ConvertPrometheusSrv {
 	return &ConvertPrometheusSrv{
 		cfg:              cfg,
@@ -130,6 +146,7 @@ func NewConvertPrometheusSrv(
 		datasourceCache:  datasourceCache,
 		alertRuleService: alertRuleService,
 		featureToggles:   featureToggles,
+		am:               am,
 	}
 }
 
@@ -518,7 +535,47 @@ func (srv *ConvertPrometheusSrv) RouteConvertPrometheusPostAlertmanagerConfig(c
 }
 
 func (srv *ConvertPrometheusSrv) RouteConvertPrometheusGetAlertmanagerConfig(c *contextmodel.ReqContext) response.Response {
-	return response.Error(http.StatusNotImplemented, "Not Implemented", nil)
+	if !srv.featureToggles.IsEnabledGlobally(featuremgmt.FlagAlertingImportAlertmanagerAPI) {
+		return response.Error(http.StatusNotImplemented, "Not Implemented", nil)
+	}
+
+	logger := srv.logger.FromContext(c.Req.Context())
+	ctx := c.Req.Context()
+
+	identifier, err := parseConfigIdentifierHeader(c)
+	if err != nil {
+		logger.Error("failed to parse config identifier header", "err", err)
+		return errorToResponse(err)
+	}
+
+	cfg, err := srv.am.GetAlertmanagerConfiguration(ctx, c.GetOrgID(), false)
+	if err != nil {
+		logger.Error("failed to get alertmanager configuration", "err", err)
+		return errorToResponse(err)
+	}
+
+	var extraCfg *apimodels.ExtraConfiguration
+	for i := range cfg.ExtraConfigs {
+		if cfg.ExtraConfigs[i].Identifier == identifier {
+			extraCfg = &cfg.ExtraConfigs[i]
+			break
+		}
+	}
+
+	if extraCfg == nil {
+		return response.Error(http.StatusNotFound, "Alertmanager configuration not found", nil)
+	}
+
+	respBody := apimodels.AlertmanagerUserConfig{
+		AlertmanagerConfig: extraCfg.AlertmanagerConfig,
+		TemplateFiles:      extraCfg.TemplateFiles,
+	}
+
+	resp := response.YAML(http.StatusOK, respBody)
+	resp.SetHeader(configIdentifierHeader, extraCfg.Identifier)
+	resp.SetHeader(mergeMatchersHeader, formatMergeMatchers(extraCfg.MergeMatchers))
+
+	return resp
 }
 
 func (srv *ConvertPrometheusSrv) RouteConvertPrometheusDeleteAlertmanagerConfig(c *contextmodel.ReqContext) response.Response {
@@ -647,3 +704,55 @@ func parseNotificationSettingsHeader(ctx *contextmodel.ReqContext) ([]models.Not
 
 	return notificationSettings, nil
 }
+
+// parseMergeMatchersHeader parses the merge matchers header value.
+// Expected format: "key1=value1,key2=value2"
+func parseMergeMatchersHeader(c *contextmodel.ReqContext) (amconfig.Matchers, error) {
+	matchersStr := strings.TrimSpace(c.Req.Header.Get(mergeMatchersHeader))
+
+	if matchersStr == "" {
+		return amconfig.Matchers{}, errInvalidHeaderValue(mergeMatchersHeader, errors.New("value cannot be empty"))
+	}
+
+	matchers := amconfig.Matchers{}
+
+	for pair := range strings.SplitSeq(matchersStr, ",") {
+		parts := strings.SplitN(strings.TrimSpace(pair), "=", 2)
+		if len(parts) != 2 {
+			return nil, errInvalidHeaderValue(mergeMatchersHeader, errors.New("format should be 'key=value,key2=value2'"))
+		}
+
+		key := strings.TrimSpace(parts[0])
+		value := strings.TrimSpace(parts[1])
+
+		if key == "" || value == "" {
+			return nil, errInvalidHeaderValue(mergeMatchersHeader, errors.New("keys and values cannot be empty"))
+		}
+
+		matchers = append(matchers, &labels.Matcher{
+			Type:  labels.MatchEqual,
+			Name:  key,
+			Value: value,
+		})
+	}
+
+	return matchers, nil
+}
+
+func formatMergeMatchers(matchers amconfig.Matchers) string {
+	var pairs []string
+	for _, matcher := range matchers {
+		if matcher.Type == labels.MatchEqual {
+			pairs = append(pairs, fmt.Sprintf("%s=%s", matcher.Name, matcher.Value))
+		}
+	}
+	return strings.Join(pairs, ",")
+}
+
+func parseConfigIdentifierHeader(c *contextmodel.ReqContext) (string, error) {
+	identifier := strings.TrimSpace(c.Req.Header.Get(configIdentifierHeader))
+	if identifier == "" {
+		return "", errInvalidHeaderValue(configIdentifierHeader, errors.New("identifier cannot be empty"))
+	}
+	return identifier, nil
+}