As you want to be alerted when there are no pull message operations you'll have to use the subscription/pull_request_count metric. If, after some time, the metric is dropped instead of reporting 0 pulls you can use two conditions: is absent for 3 minutes OR is below 1 for 1 minute:
However, the problem here is that the UI filters out all unused resources and metrics (for the past 6 weeks). While this greatly eases out setting alerts and browsing through metrics for running operations it requires a different approach to create new alerts before a system is in production. The easiest solution is to make a dummy subscription and pull messages so that the metric appears.
But you can still use the Stackdriver Monitoring API to set them up (I actually tested this with a Spanner metric in a workspace with no instances for the last few months). Keep in mind that the alerting policies API is in Beta so it's subject to non-backwards-compatible changes.
I'd recommend to start by inspecting an already existing policy with projects.alertPolicies/list and see how the AlertPolicy body is constructed.
Then you can set some initial variables:
TOKEN="$(gcloud auth print-access-token)"
PROJECT=$(gcloud config get-value project 2>\dev\null)
SUBSCRIPTION=PUBSUB_SUBSCRIPTION_ID
CHANNEL=NOTIFICATION_CHANNEL_ID
In my case I am monitoring only a specific Pub/Sub subscription throughout the example and I already had a notification channel (for my email). As you also have an existing policy you can get the notification channel ID here.
With projects.alertPolicies/create you can create the new alert policy:
curl -X POST \
-H "Authorization: Bearer $TOKEN" \
-H "Content-Type: application/json" \
"https://monitoring.googleapis.com/v3/projects/$PROJECT/alertPolicies" \
-d @alert.json
where alert.json is (replace the variables as needed):
{
"displayName": "no-pull-alert",
"combiner": "OR",
"conditions": [
{
"conditionAbsent": {
"filter": "metric.type=\"pubsub.googleapis.com/subscription/pull_request_count\" resource.type=\"pubsub_subscription\" resource.label.\"project_id\"=\"$PROJECT\" resource.label.\"subscription_id\"=\"$SUBSCRIPTION\"",
"duration": "180s",
"trigger": {
"count": 1
},
"aggregations": [
{
"alignmentPeriod": "60s",
"perSeriesAligner": "ALIGN_RATE"
}
]
},
"displayName": "Pull requests absent for $PROJECT, $SUBSCRIPTION"
},
{
"conditionThreshold": {
"filter": "metric.type=\"pubsub.googleapis.com/subscription/pull_request_count\" resource.type=\"pubsub_subscription\" resource.label.\"project_id\"=\"$PROJECT\" resource.label.\"subscription_id\"=\"$SUBSCRIPTION\"",
"comparison": "COMPARISON_LT",
"thresholdValue": 1,
"duration": "60s",
"trigger": {
"count": 1
},
"aggregations": [
{
"alignmentPeriod": "60s",
"perSeriesAligner": "ALIGN_RATE"
}
]
},
"displayName": "Pull requests are 0 for $PROJECT, $SUBSCRIPTION"
}
],
"documentation": {
"content": "**ALERT**\n\nNo pull message operations",
"mimeType": "text/markdown"
},
"notificationChannels": [
"projects/$PROJECT/notificationChannels/$CHANNEL"
],
"enabled": true
}
Briefly, you don't need to pass policy or condition IDs as those will be populated by the API. Use OR as the combiner (policy violates when ANY condition is met) to trigger the alert when the metric is either absent (conditionAbsent) or below 1 (conditionThreshold). And, of course, you can modify parameters to better suit your use case, display names, descriptions, etc.
num_undelivered_messages. You should include these use-cases in your question because there are very relevant! Anyway, it seems thatsubscription/pull_request_countis the metric you want to use here. Have you found why this metric does not generate data sometimes? Could you clarify what "alerting break once there is no data" means? Is the alert triggered? How does your alert is configured now? Please add these information to your question, it may help other people to find out what is going on. – norbjdis absentas the policy condition instead ofis under 1? Minimum seems to be 3 min though. – Guillem Xercavins