thanos-ruler: set default retention from UWM Prometheus if present

If no thanos ruler retention is set, but UWM Prometheus retention is
set, use the Prometheus retention as the thanos ruler retention. Setting
thanos ruler retention explicitly overrides this.

Signed-off-by: Jan Fajerski <[email protected]>
generated-with-ai: cursor

Author: jan--f

pkg/manifests/config.go

@@ -664,6 +664,13 @@ func (u *UserWorkloadConfiguration) applyDefaults() {
 	if u.ThanosRuler == nil {
 		u.ThanosRuler = &ThanosRulerConfig{}
 	}
+	// If the user configured a retention for user-workload Prometheus but did not
+	// explicitly set a retention for Thanos Ruler, default Thanos Ruler retention
+	// to the same value as Prometheus. This keeps the effective retention aligned
+	// unless the user overrides it for Thanos Ruler.
+	if u.ThanosRuler.Retention == "" && u.Prometheus != nil && u.Prometheus.Retention != "" {
+		u.ThanosRuler.Retention = u.Prometheus.Retention
+	}
 	if u.Alertmanager == nil {
 		u.Alertmanager = &AlertmanagerUserWorkloadConfig{}
 	}

pkg/manifests/config_test.go

@@ -261,6 +261,34 @@ thanosRuler:
 				return ``
 			},
 		},
+		{
+			name: "thanosRuler.retention defaults to prometheus.retention when unset",
+			configString: func() string {
+				return `
+prometheus:
+  retention: 15d
+`
+			},
+			configCheck: func(uwmc *UserWorkloadConfiguration) {
+				require.Equal(t, "15d", uwmc.Prometheus.Retention)
+				require.Equal(t, "15d", uwmc.ThanosRuler.Retention)
+			},
+		},
+		{
+			name: "explicit thanosRuler.retention overrides prometheus.retention",
+			configString: func() string {
+				return `
+prometheus:
+  retention: 15d
+thanosRuler:
+  retention: 7d
+`
+			},
+			configCheck: func(uwmc *UserWorkloadConfiguration) {
+				require.Equal(t, "15d", uwmc.Prometheus.Retention)
+				require.Equal(t, "7d", uwmc.ThanosRuler.Retention)
+			},
+		},
 	}
 
 	for _, tc := range tcs {

pkg/manifests/manifests_test.go

@@ -4305,6 +4305,36 @@ func TestThanosRulerRetentionConfig(t *testing.T) {
 	}
 }
 
+func TestThanosRulerRetentionDefaultsToPrometheusRetention(t *testing.T) {
+	// Construct a user-workload configuration the same way the operator does in
+	// production, i.e. via NewUserConfigFromString, so that UserWorkloadConfiguration
+	// defaulting (including retention alignment) is applied.
+	uwc, err := NewUserConfigFromString(`
+prometheus:
+  retention: 45d
+`)
+	require.NoError(t, err)
+
+	c := NewDefaultConfig()
+	c.UserWorkloadConfiguration = uwc
+
+	f := NewFactory("openshift-monitoring", "openshift-user-workload-monitoring", c, defaultInfrastructureReader(), &fakeProxyReader{}, NewAssets(assetsPath), &APIServerConfig{}, &configv1.Console{})
+
+	tr, err := f.ThanosRulerCustomResource(
+		&v1.Secret{ObjectMeta: metav1.ObjectMeta{Name: "foo"}},
+		nil,
+	)
+
+	if err != nil {
+		t.Fatalf("Unexpected error occured %v", err)
+		return
+	}
+
+	if tr.Spec.Retention != "45d" {
+		t.Fatalf("Retention is not configured correctly, expected %s, got %s", "45d", tr.Spec.Retention)
+	}
+}
+
 func TestPrometheusGoGCRelatedConfig(t *testing.T) {
 	for _, tc := range []struct {
 		ir    InfrastructureReader