Alert Rule (dead letter queue) does not trigger

Question

Alert Rule (dead letter queue) does not trigger

Benjamin Weber 71

I have an alert rule in place that informs me when there is a Azure service bus queue message in the deadletter.

This worked fine for years, but since a few days, the rule does not trigger any longer.

What I tried so far:

Recreate the rule
Adjust the conditions (timeframe)
Enable/disable the rule

What else can I try? In the conditions-editing, it shows that the conditions are correct:

CleanShot 2025-09-10 at 12.33.14

However, the alert never fires:

CleanShot 2025-09-10 at 12.33.48

Please help with this, thanks!

Suchitra Suregaunkar 14,595 Reputation points Microsoft External Staff Moderator

2025-09-10T15:42:51.7833333+00:00

Hello Benjamin Weber,

Thank you for posting your query on Microsoft Q&A portal.

If you believe a metric alert should have fired but it didn't, and it isn't listed in the Azure portal, try the following steps:

Review the metric alert rule configuration.

Check that Aggregation type and Aggregation granularity (Period) are configured as expected. Aggregation type determines how metric values are aggregated. Aggregation granularity (Period) controls how far back the evaluation aggregates the metric values each time the alert rule runs.

Check that Threshold value or Sensitivity are configured as expected.

For an alert rule that uses Dynamic Thresholds, check if advanced settings are configured. Number of violations might filter alerts, and Ignore data before can affect how the thresholds are calculated. Check if the alert fired but didn't send the notification.

Review the fired alerts list to see if you can locate the fired alert. If you can see the alert in the list but have an issue with some of its actions or notifications.

Check if the alert is already active.

Check if there's already a fired alert on the metric time series for which you expected to get an alert. Metric alerts are stateful by default, which means that once an alert is fired on a specific metric time series, more alerts on that time series won't be fired until the issue is no longer observed. This design choice reduces noise. The alert is resolved automatically when the alert condition isn't met for three consecutive evaluations.

Check the dimensions used.

If you've selected some dimension values for a metric, the alert rule monitors each individual metric time series (as defined by the combination of dimension values) for a threshold breach. To also monitor the aggregate metric time series, without any dimensions selected, configure another alert rule on the metric without selecting dimensions.

Check the aggregation and time granularity.

If you're using metrics charts, ensure that:

The selected Aggregation in the metric chart is the same as Aggregation type in your alert rule.

The selected Time granularity is the same as Aggregation granularity (Period) in your alert rule, and isn't set to Automatic.

Check if the alert rule is missing the first evaluation period in a time series.

You can reduce the likelihood of missing the first evaluation of added time series by making sure that you choose an Aggregation granularity (Period) that's larger than the Frequency of evaluation in the following cases:

When a new dimension value combination is added to a metric alert rule that monitors multiple dimensions.

When a new resource is added to the scope to a metric alert rule that monitors multiple resources.

When the metric is emitted after a period longer than 24 hours in which it wasn't emitted for metric alert rule that monitors a metric that isn't emitted continuously (sparse metric).

Reference: https://learn.microsoft.com/en-us/azure/azure-monitor/alerts/alerts-troubleshoot-metric#metric-alert-didnt-fire-when-it-should-have

Thanks,

Suchitra.
Benjamin Weber 71 Reputation points

2025-09-11T06:20:01.0733333+00:00

Hello @Suchitra Suregaunkar , I went through your list of ideas and checked everything, none of them applied. What else can I try? My next idea is to remove the alert for a day or two and re-create it then
Suchitra Suregaunkar 14,595 Reputation points Microsoft External Staff Moderator

2025-09-12T08:56:56.31+00:00

Hello Benjamin Weber, Could you please let me know the exact repro steps you followed to set up an alert?

Benjamin Weber 71

@Suchitra Suregaunkar I created it via Terraform; see code below. This worked in the past. I tried via Azure Portal as well, but it did not work either.

Edit: I tried without dimensions as well, this did not help either.

resource "azurerm_monitor_metric_alert" "deadLetter" {
  name                = "DeadLetterAlert ${var.env}"
  resource_group_name = var.rgName
  scopes              = [azurerm_servicebus_namespace.main.id]
  description         = "DeadLetter entry in service bus"
  enabled             = var.env != "dev"
  severity            = 0
  frequency           = "PT5M" // 5min
  window_size         = "PT15M"
  auto_mitigate       = true


  criteria {
    threshold        = 0
    metric_namespace = "Microsoft.ServiceBus/namespaces"
    metric_name      = "DeadletteredMessages"
    operator         = "GreaterThan"
    aggregation      = "Maximum"
    dimension {
      name     = "EntityName"
      operator = "Include"
      values   = ["*"]
    }
  }

  action {
    action_group_id    = var.actionGroupId
    webhook_properties = {}
  }
}

Suchitra Suregaunkar 14,595 Reputation points Microsoft External Staff Moderator

2025-09-16T08:56:17.2133333+00:00

Hello Benjamin Weber, We have reached out to you for few of the details via private message, could you please share it?

Thanks,

Suchitra.
Tim Bouveng 0 Reputation points

2025-09-17T07:15:31.0633333+00:00

Hi @Suchitra Suregaunkar ,

We're also experiencing exactly the same issue as above. We've tried the above remedies, creating manual rules, adjusting conditions/dimensions etc. When previewing the condition in the alert it shows that it should trigger, but nothing actually does. What was shared i private messages so far? Any ideas what is wrong?
Benjamin Weber 71 Reputation points

2025-09-17T07:24:54.7666667+00:00

So far, I was only asked for lots of information which I provided
Tim Bouveng 0 Reputation points

2025-09-17T12:05:49.8066667+00:00
Have you tried other alert rules on the servicebus resource, like count active messages etc? During our testing that didn't work either, however alerts on anything other than servicebus works. For us it started around the 4th of september, how about you?

What we have tried without success:

Creating alerts with and w/o state (autoresolve)

Alerts on different metrics on the servicebus resource

Disable all other rules leaving just one

Created a new servicebus resource with only one alert rule

Alerts based on all combinations of condition/dimension, limiting on one specific or all queues etc.

Using the exact same rule on a completely different account/subscription works. Any findings from your end?
Tim Bouveng 0 Reputation points

2025-09-17T13:15:37.9133333+00:00

We defaulted to another region when testing on another subscription, are you perhaps also running servicebus in 'North Europe'? Alerts trigger fine for 'Sweden Central' for instance, but not for 'North Europe', created new servicesbus instances and alerts for both regions to verify.
Paul de Vries 0 Reputation points

2025-09-19T14:12:29.1966667+00:00

I have exactly the same issue with a servicebus in West Europe. It does not respond to the alerts.
Is there any update on this issue?
Benjamin Weber 71 Reputation points

2025-09-22T13:23:46.6366667+00:00

Interesting to hear that other people have the same issue!

The backend support team informed me that they are looking into this, but no further info so far.

@Tim Bouveng It started around the 4th of September for us as well! Other alerts work for us, but we do not have any other alert on the same service bus. Our bus runs in West Europe.

3 answers

Your answer

Benjamin Weber 71 Reputation points

2025-09-11T06:20:01.0733333+00:00

Hello @Suchitra Suregaunkar , I went through your list of ideas and checked everything, none of them applied. What else can I try? My next idea is to remove the alert for a day or two and re-create it then
Suchitra Suregaunkar 14,595 Reputation points Microsoft External Staff Moderator

2025-09-12T08:56:56.31+00:00

Hello Benjamin Weber, Could you please let me know the exact repro steps you followed to set up an alert?
Benjamin Weber 71 Reputation points

2025-09-12T17:18:27.2966667+00:00

@Suchitra Suregaunkar I created it via Terraform; see code below. This worked in the past. I tried via Azure Portal as well, but it did not work either.

Edit: I tried without dimensions as well, this did not help either.

resource "azurerm_monitor_metric_alert" "deadLetter" { name = "DeadLetterAlert ${var.env}" resource_group_name = var.rgName scopes = [azurerm_servicebus_namespace.main.id] description = "DeadLetter entry in service bus" enabled = var.env != "dev" severity = 0 frequency = "PT5M" // 5min window_size = "PT15M" auto_mitigate = true criteria { threshold = 0 metric_namespace = "Microsoft.ServiceBus/namespaces" metric_name = "DeadletteredMessages" operator = "GreaterThan" aggregation = "Maximum" dimension { name = "EntityName" operator = "Include" values = ["*"] } } action { action_group_id = var.actionGroupId webhook_properties = {} } }
Suchitra Suregaunkar 14,595 Reputation points Microsoft External Staff Moderator

2025-09-16T08:56:17.2133333+00:00

Hello Benjamin Weber, We have reached out to you for few of the details via private message, could you please share it?

Thanks,

Suchitra.
Tim Bouveng 0 Reputation points

2025-09-17T07:15:31.0633333+00:00

Hi @Suchitra Suregaunkar ,

We're also experiencing exactly the same issue as above. We've tried the above remedies, creating manual rules, adjusting conditions/dimensions etc. When previewing the condition in the alert it shows that it should trigger, but nothing actually does. What was shared i private messages so far? Any ideas what is wrong?
Benjamin Weber 71 Reputation points

2025-09-17T07:24:54.7666667+00:00

So far, I was only asked for lots of information which I provided
Tim Bouveng 0 Reputation points

2025-09-17T12:05:49.8066667+00:00

Have you tried other alert rules on the servicebus resource, like count active messages etc? During our testing that didn't work either, however alerts on anything other than servicebus works. For us it started around the 4th of september, how about you?

What we have tried without success:

Creating alerts with and w/o state (autoresolve)

Alerts on different metrics on the servicebus resource

Disable all other rules leaving just one

Created a new servicebus resource with only one alert rule

Alerts based on all combinations of condition/dimension, limiting on one specific or all queues etc.

Using the exact same rule on a completely different account/subscription works. Any findings from your end?
Tim Bouveng 0 Reputation points

2025-09-17T13:15:37.9133333+00:00

We defaulted to another region when testing on another subscription, are you perhaps also running servicebus in 'North Europe'? Alerts trigger fine for 'Sweden Central' for instance, but not for 'North Europe', created new servicesbus instances and alerts for both regions to verify.
Paul de Vries 0 Reputation points

2025-09-19T14:12:29.1966667+00:00

I have exactly the same issue with a servicebus in West Europe. It does not respond to the alerts.
Is there any update on this issue?
Benjamin Weber 71 Reputation points

2025-09-22T13:23:46.6366667+00:00

Interesting to hear that other people have the same issue!

The backend support team informed me that they are looking into this, but no further info so far.

@Tim Bouveng It started around the 4th of September for us as well! Other alerts work for us, but we do not have any other alert on the same service bus. Our bus runs in West Europe.

Answer 1

Benjamin Weber 71

And suddenly it stopped working again :/

Am I the only one?

Tim Bouveng 0 Reputation points

2025-11-20T12:28:20.03+00:00

It's still working for us, but I guess we'll have to keep an extra eye on it again :/
Benjamin Weber 71 Reputation points

2025-11-20T12:57:59.6766667+00:00

It works again now, just skipped for like one day... Quite annoying
Tim Bouveng 0 Reputation points

2025-11-20T13:07:09.39+00:00

We had no deadletters in our service yesterday, maybe it was during that day and we got lucky?

Answer 2

Paul de Vries 0

Yes, same for me. It also started working again

0 comments

Answer 3

Benjamin Weber 71

@Suchitra Suregaunkar Without me changing anything, the rule started working again!

Tim Bouveng 0 Reputation points

2025-09-25T05:55:40.2366667+00:00

Same here, at first we got a few of them but not all, but everything seems to trigger just fine now.

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Alert Rule (dead letter queue) does not trigger

3 answers

Your answer