Cannot run .NET Core application on Linux in Azure App Services with linuxFxVersion: 'DOTNETCORE:8.0'

Question

When I define my .NET Core application to run on Linux in Azure App Services with linuxFxVersion: 'DOTNETCORE:8.0' and reserved: true, I keep getting HTTP 404 responses from Nginx.

The application works fine on Windows in Azure App Services.

Looking at the logs, it seems like App Services is downloading a PHP image, which outputs a version of PHP 8.0.x.

Has anyone experienced something similar and knows how to fix it?

Code:

resource appServicePlan 'Microsoft.Web/serverfarms@2022-03-01' = {
  name: appServicePlanName
  location: location
  sku: environmentConfigurationMap[environment].appServicePlan.sku
  properties: {
    reserved: true
  }
  kind: 'linux'
}

resource appServiceApp 'Microsoft.Web/sites@2022-03-01' = {
  name: appServiceAppName
  location: location
  identity: { type: 'SystemAssigned' }
  properties: {
    serverFarmId: appServicePlan.id
    httpsOnly: true
    siteConfig: {
      linuxFxVersion: 'DOTNETCORE:8.0'
      // netFrameworkVersion: 'v8.0'
      appSettings: [
        {
          name: 'APPINSIGHTS_INSTRUMENTATIONKEY'
          value: applicationInsights.properties.InstrumentationKey
        }
        {
          name: 'APPLICATIONINSIGHTS_CONNECTION_STRING'
          value: applicationInsights.properties.ConnectionString
        }
      ]
    }
  }
}

Error:

Answer 1

The right syntax for setting a .NET version in linuxFxVersion is DOTNETCORE|x.x, even for .NET 6 or .NET 8.

So instead of:

DOTNETCORE:8.0

Use:

DOTNETCORE|8.0

Available built-in stacks for Web Apps and Function Apps

You can run the az webapp list-runtimes to list the available built-in stacks which can be used for web apps, but as mentioned in the comments of the question this list doesn't seem to be correct (: is not the right separator):

C:\Users\ruija> az webapp list-runtimes --os-type linux --output table

Result
--------------------------
DOTNETCORE:9.0
DOTNETCORE:8.0
DOTNETCORE:7.0
DOTNETCORE:6.0
NODE:20-lts
NODE:18-lts
NODE:16-lts
PYTHON:3.12
PYTHON:3.11
PYTHON:3.10
PYTHON:3.9
PYTHON:3.8
PHP:8.3
PHP:8.2
PHP:8.1
PHP:8.0
JAVA:21-java21
JAVA:17-java17
JAVA:11-java11
JAVA:8-jre8
JBOSSEAP:8-java17
JBOSSEAP:8-java11
JBOSSEAP:8.0.2-java17_byol
JBOSSEAP:8.0.2-java11_byol
JBOSSEAP:7-java17
JBOSSEAP:7-java11
JBOSSEAP:7-java8
TOMCAT:10.1-java21
TOMCAT:10.1-java17
TOMCAT:10.1-java11
TOMCAT:10.0-java17
TOMCAT:10.0-java11
TOMCAT:10.0-jre8
TOMCAT:9.0-java21
TOMCAT:9.0-java17
TOMCAT:9.0-java11
TOMCAT:9.0-jre8
TOMCAT:8.5-java11
TOMCAT:8.5-jre8

Running the equivalent command for Function Apps (az functionapp list-runtimes) returns a different list:

PS C:\Users\myself> az functionapp list-runtimes --os linux --query "[].linux_fx_version" --output table

Result
-------------------
DOTNET-ISOLATED|9.0
DOTNET-ISOLATED|8.0
DOTNET-ISOLATED|7.0
DOTNET-ISOLATED|6.0
DOTNET|8.0
DOTNET|6.0
Node|22
Node|20
Node|18
Python|3.11
Python|3.10
Python|3.9
Python|3.8
Python|3.7
Java|21
Java|17
Java|11
Java|8
PowerShell|7.4
PowerShell|7.2