[BUG]: AzureFunctionApp@2 - 400 BadRequest warning on every Flex Consumption deployment due to FunctionAppScaleLimit in config update

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Task name

AzureFunctionApp

Task version

2.275.1

Issue Description

When deploying to a Flex Consumption (FC1) function app using AzureFunctionApp@2 with isFlexConsumption: true, the task emits a ##[warning] on every run due to a 400 BadRequest from the ARM API during the post-deploy configuration update step.

Expected: Deployment completes with no warnings. When isFlexConsumption: true is set, the task should not attempt to write configuration properties that are invalid for Flex Consumption sites.

Actual: The following warning is emitted after every deployment:

##[warning]Failed to update App Service configuration details. Error: Error: Failed to up/date App service 'func-*' configuration. Error: BadRequest - The following site configuration property (Site.SiteConfig.FunctionAppScaleLimit) for Flex Consumption sites is invalid. Please remove or rename it before retrying. (CODE: 400)

The zip deployment itself succeeds; only the post-deploy config update step fails.

Function app created with bicep deployed using #AzureResourceManagerTemplateDeployment@3 task:

resource functionApp 'Microsoft.Web/sites@2025-03-01' = {
  name: functionAppName
  location: location
  kind: 'functionapp,linux'
  identity: {
    type: 'SystemAssigned'
  }
  properties: {
    clientAffinityEnabled: false
    serverFarmId: hostingPlan.id
    httpsOnly: true
    functionAppConfig: {
      deployment: {
        storage: {
          type: 'blobContainer'
          value: '${storageAccount.properties.primaryEndpoints.blob}${deploymentContainerName}'
          authentication: {
            type: 'SystemAssignedIdentity'
          }
        }
      }
      scaleAndConcurrency: {
        maximumInstanceCount: 40
        instanceMemoryMB: 512
        triggers: {
          http: {
            perInstanceConcurrency: 4
          }
        }
      }
      runtime: {
        name: 'dotnet-isolated'
        version: '8.0'
      }
    }
  }
  dependsOn: [
    deploymentContainer
  ]
}

Environment type (Please select at least one enviroment where you face this issue)

• Self-Hosted
• Microsoft Hosted
• VMSS Pool
• Container

Azure DevOps Server type

dev.azure.com (formerly visualstudio.com)

Azure DevOps Server Version (if applicable)

No response

Operation system

Image: ubuntu-24.04 Version: 20260607.184.1

Relevant log output

Starting: Deploy Function App
==============================================================================
Task         : Azure Functions Deploy
Description  : Update a function app with .NET, Python, JavaScript, PowerShell, Java based web applications
Version      : 2.275.1
Author       : Microsoft Corporation
Help         : https://aka.ms/azurefunctiontroubleshooting
==============================================================================
Got service connection details for Azure App Service:'****'
The Deployment Type option does not apply for Flex Consumption.
##[warning]Failed to update App Service configuration details. Error: Error: Failed to update App service '****' configuration. Error: BadRequest - The following site configuration property (Site.SiteConfig.FunctionAppScaleLimit) for Flex Consumption sites is invalid.  Please remove or rename it before retrying. (CODE: 400)
    at AzureAppService.<anonymous> (/home/vsts/work/_tasks/AzureFunctionApp_501dd25d-1785-43e4-b4e5-a5c78ccc0573/2.275.1/node_modules/azure-pipelines-tasks-azure-arm-rest/azure-arm-app-service.js:543:23)
    at Generator.next (<anonymous>)
    at fulfilled (/home/vsts/work/_tasks/AzureFunctionApp_501dd25d-1785-43e4-b4e5-a5c78ccc0573/2.275.1/node_modules/azure-pipelines-tasks-azure-arm-rest/azure-arm-app-service.js:5:58)
    at process.processTicksAndRejections (node:internal/process/task_queues:104:5)
Successfully added release annotation to the Application Insight : ****
App Service Application URL: https://****.azurewebsites.net
Finishing: Deploy Function App

Full task logs with system.debug enabled

Details

 [REPLACE THIS WITH YOUR INFORMATION] 

Repro steps

- task: AzureFunctionApp@2
  inputs:
    connectedServiceNameARM: '<service-connection>'
    appType: functionAppLinux
    isFlexConsumption: true
    appName: '<function-app-name>'
    package: '<path-to-deployment.zip>'

[spatelshield]

ghcp analysis below if it is helpful.

---

Root Cause

FlexConsumptionWebAppDeploymentProvider.DeployWebAppStep() deploys the zip via kuduServiceUtility.oneDeployFlex(), then calls the inherited PostDeploymentStep() from AzureRmWebAppDeploymentProvider without overriding it.

AzureRmWebAppDeploymentProvider.PostDeploymentStep() unconditionally calls this.appServiceUtilityExt.updateScmTypeAndConfigurationDetails() — there is no isFlexConsumption guard:

// AzureRmWebAppDeploymentProvider.ts
protected async PostDeploymentStep() {
    if (this.taskParams.AppSettings) {
        var customApplicationSettings = ParameterParser.parse(this.taskParams.AppSettings);
        await this.appServiceUtility.updateAndMonitorAppSettings(customApplicationSettings);
    }
    await this.appServiceUtilityExt.updateScmTypeAndConfigurationDetails(); // ← no FC guard
}

updateScmTypeAndConfigurationDetails() in AzureAppServiceUtilityExt.ts reads the full site config via GET .../config/web, modifies scmType, then writes the entire object back via PUT .../config/web:

// AzureAppServiceUtilityExt.ts
var configDetails = await this._appService.getConfiguration();
// configDetails.properties contains functionAppScaleLimit on FC sites
if (scmType && scmType.toLowerCase() === "none") {
    configDetails.properties.scmType = 'VSTSRM';
    await this._appService.updateConfiguration(configDetails); // ← ARM rejects functionAppScaleLimit → 400
}

The ARM API for Flex Consumption sites rejects Site.SiteConfig.FunctionAppScaleLimit on PUT .../config/web, returning 400 BadRequest. The property is present in the GET response but is read-only / invalid for FC sites on write.

The same file already has a correct Flex Consumption guard in UpdateDeploymentStatus():

// AzureRmWebAppDeploymentProvider.ts — guard exists here but not in PostDeploymentStep
if (this.kuduServiceUtility && !this.taskParams.isFlexConsumption) {
    this.activeDeploymentID = await this.kuduServiceUtility.updateDeploymentStatus(...);
}

The pattern is established — it just wasn't applied to PostDeploymentStep().

---

Suggested fix

Option A (preferred — lowest risk): Override PostDeploymentStep() in FlexConsumptionWebAppDeploymentProvider

Skip updateScmTypeAndConfigurationDetails() entirely for Flex Consumption deployments, matching the existing guard pattern used in UpdateDeploymentStatus().

// FlexConsumptionWebAppDeploymentProvider.ts
protected async PostDeploymentStep() {
    if (this.taskParams.AppSettings) {
        var customApplicationSettings = ParameterParser.parse(this.taskParams.AppSettings);
        await this.appServiceUtility.updateAndMonitorAppSettings(customApplicationSettings);
    }
    // updateScmTypeAndConfigurationDetails() intentionally skipped:
    // Flex Consumption sites reject Site.SiteConfig.FunctionAppScaleLimit on PUT config/web (400 BadRequest).
}

Option B: Strip the invalid property before writing in updateScmTypeAndConfigurationDetails()

Handles the case defensively inside the utility, so any future deployment provider that calls this method for an FC site is also protected.

// AzureAppServiceUtilityExt.ts
if (scmType && scmType.toLowerCase() === "none") {
    configDetails.properties.scmType = 'VSTSRM';
    delete configDetails.properties.functionAppScaleLimit; // FC sites reject this on PUT
    await this._appService.updateConfiguration(configDetails);
}