Build .NET 5 Azure Functions with Azure DevOps pipeline

I believe most of us already migrate our Azure Functions from older .NET version to .NET 5!! And most of us uses Azure DevOps to build them, am I right?

I encounter an issue when I build the function app so I like to share it so that others won't suffer from the issue.

Issue

When using Azure DevOps pipeline to build Azure Function with .NET 5, I encountered following error.

[error]/home/vsts/.nuget/packages/microsoft.net.sdk.functions/3.0.11/build/Microsoft.NET.Sdk.Functions.Build.targets(32,5): Error : It was not possible to find any compatible framework version
The framework 'Microsoft.NETCore.App', version '3.1.0' was not found.

Cause

The root cause is that I need both .NET Core 3 and .NET 5 to successfully build the application. Therefore, I simply need to add UseDotNet task twice with different versions!

- task: UseDotNet@2
  displayName: 'Use .NET Core 3.1 sdk'
  inputs:
    packageType: sdk
    version: '3.1.x'

- task: UseDotNet@2
  displayName: 'Use .NET 5 sdk'
  inputs:
    packageType: sdk
    version: '5.0.x'

I hope we can build the app only with .NET 5 SDK in the near future, as this was a bit confusing :)

Reference

Stackoverflow:.NET 5 - The framework 'Microsoft.NETCore.App', version '3.1.0' was not found