Edit

Override auto-generated KEDA scale rules for Azure Functions on Container Apps

Functions on Container Apps normally runs in platform-managed scaling mode. At startup, the Functions host inspects triggers (for example, HTTP, Queue, or Timer), and Azure Container Apps creates the matching KEDA trigger configuration for the app revision.

Set properties.template.scale.allowScalingRuleOverride when you want to disable that automatic mapping and provide your own scale rules in template.scale.rules.

Prerequisites

  • A Container Apps resource deployed as a Functions app (kind=functionapp).
  • The Azure CLI, with permission to call az rest against the app resource.
  • REST API version 2026-03-02-preview or newer.

Property definition

Property Type Default Applies to API version
properties.template.scale.allowScalingRuleOverride boolean (nullable) false / null Functions on Container Apps only (kind=functionapp) 2026-03-02-preview and later

Behavior

Override value Scale rules Behavior
false or null Auto-generated Azure creates and manages KEDA rules from discovered Functions triggers. User-supplied rules are blocked in this mode.
true Customer-defined Azure doesn't generate trigger-based rules. The rules you provide are used for scale decisions.
true with no rules provided None provided Azure skips trigger-based rule generation. Only the platform's baseline HTTP scaler behavior remains active.

Enable override and provide custom scale rules

This example starts with platform-managed scaling (allowScalingRuleOverride=false) and switches to manual rule control. The PATCH request includes one Azure Queue rule and one HTTP concurrency rule.

  1. Create a PATCH body file named patch-enable-override.json.

    {
  "properties": {
    "template": {
      "scale": {
        "allowScalingRuleOverride": true,
        "rules": [
          {
            "name": "my-queue-rule",
            "custom": {
              "type": "azure-queue",
              "metadata": {
                "queueName": "my-test-queue",
                "queueLength": "20",
                "connectionFromEnv": "AzureWebJobsStorage"
              }
            }
          },
          {
            "name": "my-http-rule",
            "http": {
              "metadata": {
                "concurrentRequests": "50"
              }
            }
          }
        ]
      }
    }
  }
}

  2. Apply the update.

    az rest --method PATCH \
  --uri "https://management.azure.com/subscriptions/{subscriptionId}/resourceGroups/{resourceGroup}/providers/Microsoft.App/containerApps/{appName}?api-version=2026-03-02-preview" \
  --headers "Content-Type=application/json" \
  --body @patch-enable-override.json

Expected outcome:

  • Trigger-derived rules aren't generated for the new revision.
  • The custom rules (my-queue-rule and my-http-rule) are attached to the revision.
  • Scale-out behavior now follows queue depth (queueLength=20) and HTTP concurrency (concurrentRequests=50).

Disable override and revert to platform-generated rules

This example returns a manually configured app (allowScalingRuleOverride=true) to platform-managed scaling.

Important

A request that sets allowScalingRuleOverride=false while rules is non-empty is rejected. To switch back, send rules: [] in the same PATCH.

  1. Create a PATCH body file named patch-disable-override.json.

    {
  "properties": {
    "template": {
      "scale": {
        "allowScalingRuleOverride": false,
        "rules": []
      }
    }
  }
}

  2. Apply the update.

    az rest --method PATCH \
  --uri "https://management.azure.com/subscriptions/{subscriptionId}/resourceGroups/{resourceGroup}/providers/Microsoft.App/containerApps/{appName}?api-version=2026-03-02-preview" \
  --headers "Content-Type=application/json" \
  --body @patch-disable-override.json

Expected outcome:

  • Custom scale rules are cleared.
  • Azure resumes creating scale rules from discovered Functions triggers.
  • A new revision is produced with platform-managed scaling.

Error scenarios

Scenario Error code Error message
Set allowScalingRuleOverride=true on a non-Functions app (kind isn't functionapp) AllowScalingRuleOverrideNotApplicable The AllowScalingRuleOverride property is only applicable for Function Apps (kind = 'functionapp'). It can't be set for other container app kinds.
Set allowScalingRuleOverride=false while custom scale rules are still present FunctionAppCannotSetScaleRules Can't switch to platform-controlled mode if non-empty rules exist to protect accidentally deleting customer defined scale rules. Customers need to explicitly set [] (empty array) in scale rules if they want platform to auto-manage.

Related content

  • Last updated on