Log metric for in use hosts

terraform/alerting/monitoring.tf

@@ -221,3 +221,24 @@ EOT
     null_resource.manual-step-to-enable-workspace
   ]
 }
+
+resource "google_logging_metric" "requests_by_host" {
+  name   = "requests_by_host"
+  filter = <<-EOT
+resource.type=cloud_run_revision 
+httpRequest.requestUrl!=""
+EOT
+
+  metric_descriptor {
+    metric_kind = "DELTA"
+    value_type  = "INT64"
+    labels {
+      key        = "host"
+      value_type = "STRING"
+    }
+  }
+
+  label_extractors = {
+    "host" = "REGEXP_EXTRACT(httpRequest.requestUrl, \"^https?://([a-z0-9\\\\-._~%]+|\\\\[[a-z0-9\\\\-._~%!$&'()*+,;=:]+\\\\])/.*$\")"
+  }
+}