Add slos for rekor v2 reads

gcp/modules/monitoring/rekorv2/lb/slo.tf

@@ -0,0 +1,43 @@
+/**
+ * Copyright 2025 The Sigstore Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+module "slos" {
+  source = "../slo"
+  count  = var.create_slos ? 1 : 0
+
+  project_id            = var.project_id
+  project_number        = var.project_number
+  service_id            = "rekor_v2_global_lb_view"
+  display_name          = "Rekor V2 Reads"
+  resource_name         = "" # no telementry, this isn't a service
+  notification_channels = local.notification_channels
+
+  availability_slos = {
+    gcs-read-availability = {
+      display_prefix            = "Rekor V2 Availability"
+      base_total_service_filter = "metric.type=\"loadbalancing.googleapis.com/https/request_count\" resource.type=\"https_lb_rule\""
+      # Only count 500s as server errors since clients can trigger 400s.
+      bad_filter = "metric.labels.response_code=monitoring.regex.full_match(\"5[0-9][0-9]\")"
+      slos = {
+        api-v2-read = {
+          display_suffix = "/api/v2/{path=**} - GCS Reads"
+          label_filter   = "resource.labels.forwarding_rule_name=monitoring.regex.full_math(\".*-rekor-https-forwarding-rule\") resource.labels.matched_url_path_rule=\"/api/v2/{path=**}\""
+          goal           = 0.995
+        },
+      }
+    }
+  }
+}

gcp/modules/monitoring/rekorv2/lb/variables.tf

@@ -41,3 +41,9 @@ variable "frozen_shards" {
   type    = list(string)
   default = []
 }
+
+variable "create_slos" {
+  description = "True to enable SLO creation"
+  type        = bool
+  default     = false
+}