allow extra filter for dlq alert policy (#461)

Signed-off-by: Kenny Leung <kleung@chainguard.dev>

modules/alerting/README.md

@@ -32,6 +32,7 @@ No modules.
 
 | Name | Description | Type | Default | Required |
 |------|-------------|------|---------|:--------:|
+| <a name="input_dlq_filter"></a> [dlq\_filter](#input\_dlq\_filter) | additional filter to apply to dlq alert policy | `string` | `""` | no |
 | <a name="input_failed_req_filter"></a> [failed\_req\_filter](#input\_failed\_req\_filter) | additional filter to apply to failed request alert policy | `string` | `""` | no |
 | <a name="input_failure_rate_duration"></a> [failure\_rate\_duration](#input\_failure\_rate\_duration) | duration for condition to be active before alerting | `number` | `120` | no |
 | <a name="input_failure_rate_exclude_services"></a> [failure\_rate\_exclude\_services](#input\_failure\_rate\_exclude\_services) | List of service names to exclude from the 5xx failure rate alert | `list(string)` | `[]` | no |

modules/alerting/main.tf

@@ -382,7 +382,12 @@ resource "google_monitoring_alert_policy" "pubsub_dead_letter_queue_messages" {
 
       comparison = "COMPARISON_GT"
       duration   = "0s"
-      filter     = "metric.type=\"pubsub.googleapis.com/topic/send_request_count\" resource.type=\"pubsub_topic\" metadata.system_labels.\"name\"=~\".*-dlq-.*\""
+      filter     = <<EOT
+        metric.type="pubsub.googleapis.com/topic/send_request_count"
+        resource.type="pubsub_topic"
+        metadata.system_labels."name"=~".*-dlq-.*"
+        ${var.dlq_filter}
+      EOT
 
       trigger {
         count = "1"

modules/alerting/variables.tf

@@ -61,3 +61,9 @@ variable "failure_rate_exclude_services" {
   type        = list(string)
   default     = []
 }
+
+variable "dlq_filter" {
+  description = "additional filter to apply to dlq alert policy"
+  type        = string
+  default     = ""
+}