add initial support for alertmanager external-url (#622)

* add initial support for alertmanager external-url

* fixed test

* address review feedback - 1

cmd/operator/deploy/crds/monitoring.googleapis.com_operatorconfigs.yaml

@@ -134,6 +134,9 @@ spec:
                 required:
                 - key
                 x-kubernetes-map-type: atomic
+              externalURL:
+                type: string
+                description: ExternalURL is the URL under which Alertmanager is externally reachable (for example, if Alertmanager is served via a reverse proxy). Used for generating relative and absolute links back to Alertmanager itself. If the URL has a path portion, it will be used to prefix all HTTP endpoints served by Alertmanager. If omitted, relevant URL components will be derived automatically.
           rules:
             type: object
             description: Rules specifies how the operator configures and deployes rule-evaluator.

doc/api.md

@@ -297,6 +297,7 @@ ManagedAlertmanagerSpec holds configuration information for the managed Alertman
 | Field | Description | Scheme | Required |
 | ----- | ----------- | ------ | -------- |
 | configSecret | ConfigSecret refers to the name of a single-key Secret in the public namespace that holds the managed Alertmanager config file. | *corev1.SecretKeySelector | false |
+| externalURL | ExternalURL is the URL under which Alertmanager is externally reachable (for example, if Alertmanager is served via a reverse proxy). Used for generating relative and absolute links back to Alertmanager itself. If the URL has a path portion, it will be used to prefix all HTTP endpoints served by Alertmanager. If omitted, relevant URL components will be derived automatically. | string | false |
 
 [Back to TOC](#table-of-contents)
 

e2e/alertmanager_test.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"strings"
 	"testing"
 	"time"
 
@@ -74,6 +75,7 @@ route:
 				},
 				Key: "my-secret-key",
 			},
+			ExternalURL: "https://alertmanager.mycompany.com/",
 		},
 		&corev1.Secret{
 			ObjectMeta: metav1.ObjectMeta{
@@ -108,15 +110,15 @@ func testAlertmanager(ctx context.Context, t *OperatorContext, spec *monitoringv
 	})
 	t.Run("deployed", t.subtest(func(ctx context.Context, t *OperatorContext) {
 		t.Parallel()
-		testAlertmanagerDeployed(ctx, t)
+		testAlertmanagerDeployed(ctx, t, spec)
 	}))
 	t.Run("config set", t.subtest(func(ctx context.Context, t *OperatorContext) {
 		t.Parallel()
 		testAlertmanagerConfig(ctx, t, secret, key)
 	}))
 }
 
-func testAlertmanagerDeployed(ctx context.Context, t *OperatorContext) {
+func testAlertmanagerDeployed(ctx context.Context, t *OperatorContext, config *monitoringv1.ManagedAlertmanagerSpec) {
 	err := wait.Poll(time.Second, 1*time.Minute, func() (bool, error) {
 		var ss appsv1.StatefulSet
 		if err := t.Client().Get(ctx, client.ObjectKey{Namespace: t.namespace, Name: operator.NameAlertmanager}, &ss); err != nil {
@@ -135,6 +137,29 @@ func testAlertmanagerDeployed(ctx context.Context, t *OperatorContext) {
 			return false, fmt.Errorf("unexpected annotations (-want, +got): %s", diff)
 		}
 
+		// If config spec is empty, no need to assert EXTRA_ARGS.
+		if config == nil {
+			return true, nil
+		}
+
+		// TODO(pintohutch): clean-up wantArgs init logic.
+		var wantArgs []string
+		for _, c := range ss.Spec.Template.Spec.Containers {
+			if c.Name != "alertmanager" {
+				continue
+			}
+			// We're mainly interested in the dynamic flags but checking the entire set including
+			// the static ones is ultimately simpler.
+			if externalURL := config.ExternalURL; externalURL != "" {
+				wantArgs = append(wantArgs, fmt.Sprintf("--web.external-url=%q", config.ExternalURL))
+			}
+
+			if diff := cmp.Diff(strings.Join(wantArgs, " "), getEnvVar(c.Env, "EXTRA_ARGS")); diff != "" {
+				return false, fmt.Errorf("unexpected flags (-want, +got): %s", diff)
+			}
+			return true, nil
+		}
+
 		return true, nil
 	})
 	if err != nil {

e2e/collector_test.go

@@ -209,6 +209,7 @@ func testCollectorDeployed(ctx context.Context, t *OperatorContext) {
 			return false, fmt.Errorf("unexpected annotations (-want, +got): %s", diff)
 		}
 
+		// TODO(pintohutch): clean-up wantArgs init logic.
 		for _, c := range ds.Spec.Template.Spec.Containers {
 			if c.Name != operator.CollectorPrometheusContainerName {
 				continue

e2e/ruler_test.go

@@ -283,6 +283,7 @@ func testRuleEvaluatorDeployment(ctx context.Context, t *OperatorContext) {
 			return false, fmt.Errorf("unexpected annotations (-want, +got): %s", diff)
 		}
 
+		// TODO(pintohutch): clean-up wantArgs init logic.
 		for _, c := range deploy.Spec.Template.Spec.Containers {
 			if c.Name != "evaluator" {
 				continue

manifests/setup.yaml

@@ -986,6 +986,9 @@ spec:
                 required:
                 - key
                 x-kubernetes-map-type: atomic
+              externalURL:
+                type: string
+                description: ExternalURL is the URL under which Alertmanager is externally reachable (for example, if Alertmanager is served via a reverse proxy). Used for generating relative and absolute links back to Alertmanager itself. If the URL has a path portion, it will be used to prefix all HTTP endpoints served by Alertmanager. If omitted, relevant URL components will be derived automatically.
           rules:
             type: object
             description: Rules specifies how the operator configures and deployes rule-evaluator.

pkg/operator/apis/monitoring/v1/types.go

@@ -166,6 +166,13 @@ type ManagedAlertmanagerSpec struct {
 	// ConfigSecret refers to the name of a single-key Secret in the public namespace that
 	// holds the managed Alertmanager config file.
 	ConfigSecret *corev1.SecretKeySelector `json:"configSecret,omitempty"`
+	// ExternalURL is the URL under which Alertmanager is externally reachable
+	// (for example, if Alertmanager is served via a reverse proxy).
+	// Used for generating relative and absolute links back to Alertmanager
+	// itself. If the URL has a path portion, it will be used to prefix all HTTP
+	// endpoints served by Alertmanager.
+	// If omitted, relevant URL components will be derived automatically.
+	ExternalURL string `json:"externalURL,omitempty"`
 }
 
 // AlertmanagerEndpoints defines a selection of a single Endpoints object

pkg/operator/operator_config.go

@@ -220,10 +220,15 @@ func (r *operatorConfigReconciler) Reconcile(ctx context.Context, req reconcile.
 		return reconcile.Result{}, fmt.Errorf("ensure rule-evaluator config: %w", err)
 	}
 
+	// Ensure the alertmanager configuration is pulled from the spec.
 	if err := r.ensureAlertmanagerConfigSecret(ctx, config.ManagedAlertmanager); err != nil {
 		return reconcile.Result{}, fmt.Errorf("ensure alertmanager config secret: %w", err)
 	}
 
+	if err := r.ensureAlertmanagerStatefulSet(ctx, config.ManagedAlertmanager); err != nil {
+		return reconcile.Result{}, fmt.Errorf("ensure alertmanager statefulset: %w", err)
+	}
+
 	// Mirror the fetched secret data to where the rule-evaluator can
 	// mount and access.
 	if err := r.ensureRuleEvaluatorSecrets(ctx, secretData); err != nil {
@@ -383,6 +388,54 @@ func (r *operatorConfigReconciler) ensureAlertmanagerConfigSecret(ctx context.Co
 	return nil
 }
 
+// ensureAlertmanagerStatefulSet configures the managed Alertmanager instance
+// to reflect the provided spec.
+func (r *operatorConfigReconciler) ensureAlertmanagerStatefulSet(ctx context.Context, spec *monitoringv1.ManagedAlertmanagerSpec) error {
+	if spec == nil {
+		return nil
+	}
+
+	logger, _ := logr.FromContext(ctx)
+
+	var sset appsv1.StatefulSet
+	err := r.client.Get(ctx, client.ObjectKey{Namespace: r.opts.OperatorNamespace, Name: NameAlertmanager}, &sset)
+	// Some users deliberately not want to run the alertmanager.
+	// Only emit a warning but don't cause retries
+	// as this logic gets re-triggered anyway if the StatefulSet is created later.
+	if apierrors.IsNotFound(err) {
+		logger.Error(err, "Alertmanager StatefulSet does not exist")
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+
+	var flags []string
+	if externalURL := spec.ExternalURL; externalURL != "" {
+		flags = append(flags, fmt.Sprintf("--web.external-url=%q", externalURL))
+	}
+
+	// Set EXTRA_ARGS envvar in alertmanager container.
+	for i, c := range sset.Spec.Template.Spec.Containers {
+		if c.Name != "alertmanager" {
+			continue
+		}
+		var repl []corev1.EnvVar
+
+		for _, ev := range c.Env {
+			if ev.Name != "EXTRA_ARGS" {
+				repl = append(repl, ev)
+			}
+		}
+		repl = append(repl, corev1.EnvVar{Name: "EXTRA_ARGS", Value: strings.Join(flags, " ")})
+
+		sset.Spec.Template.Spec.Containers[i].Env = repl
+	}
+
+	// Upsert alertmanager StatefulSet.
+	return r.client.Update(ctx, &sset)
+}
+
 // ensureRuleEvaluatorDeployment reconciles the Deployment for rule-evaluator.
 func (r *operatorConfigReconciler) ensureRuleEvaluatorDeployment(ctx context.Context, spec *monitoringv1.RuleEvaluatorSpec) error {
 	logger, _ := logr.FromContext(ctx)