Issue when trying to deploy dotnet 8 web app to gcloud app engine flex

I've been using gcloud app deploy with a legacy project on dotnetcore 3.1 sometime ago. Had to go back to this project and after upgrading the project to dotnet 8 I can no longer deploy it.

Previous set of actions was:

1. dotnet publish "./SolutionName/Project.Public/Project.Public.csproj" -o "publish-api/" -c Release

   • this creates a publish folder

2. cp app-api.yaml ./publish-api/

   • copies the yaml to publish folder

3. gcloud app deploy ./publish-api/app-api.yaml --version=1.1

   • the last step now throws the next error:

   Step #2 - "build": ERROR: No buildpack groups passed detection.
   Step #2 - "build": ERROR: Please check that you are running against the correct path.
   Step #2 - "build": ERROR: failed to detect: no buildpacks participating
   

   Possibly I miss something simple here? Should I not be able to deploy from dotnet published folder?

If I try to just deploy from within a project in that solution it goes further in its build, however it also fails with a next error (for some reason it can't locate a referenced project, which lives within this solution):

  Step #2 - "build": Use 'dotnet --help' to see available commands or visit: https://aka.ms/dotnet-cli
  Step #2 - "build": --------------------------------------------------------------------------------------
  Step #2 - "build":   Determining projects to restore...
  Step #2 - "build":   Skipping project "/API.Common/API.Common.csproj" because it was not found.
  Step #2 - "build":   Skipping project "/API.Common/API.Common.csproj" because it was not found.
  Step #2 - "build":   Restored /workspace/API.csproj (in 10.28 sec).

I tried deploying a simple HelloWorld with my app.yaml consisting of just one project and that works fine. However in multi-project solution it can't find the referenced projects.

for completenes here's my deployment yaml:

    runtime: aspnetcore
    env: flex
    service: default
    
    runtime_config:
        operating_system: ubuntu22
    
    automatic_scaling:
      min_num_instances: 1
      cpu_utilization:
        target_utilization: 0.75
    
    liveness_check:
      path: "/health"
      check_interval_sec: 30
      timeout_sec: 4
      failure_threshold: 4
      success_threshold: 2
    
    resources:
      cpu: 1
      memory_gb: 1
      disk_size_gb: 10
    
    env_variables:
      GCLOUD_PROJECT_ID: proj-id

Hints or advice warmly welcome.

The issue was the that deployment tools were not understanding what to do with the published files.

Added the next to app.yaml to aid the process:

entrypoint: "dotnet Project.Public.API.dll"  # the main/starting dll 

After that running gcloud app deploy from within a published folder worked fine.