Multiple instances of the same project

[antunesl]

Hi!

In my solution I have a project that is used as a "Shell" for all modules (each module has a collection of endpoints, like a microservice), the modules to load for an instance of this are passed by configuration. So the product can behave like a monolith or scale by selecting modules to deploy in separate when needed.

The goal is to be able to have different deployment configurations based on the need of it and to grow in a easy and mor cost effective way, and then scale as needed. For example, in local dev I deploy all modules in the same running webapp, but by configuration I can run a different webapp for each module.

I'm in a process of exploring Aspire, it seems a perfect tool for this kind of distributed projects, but I'm facing a issue here when trying to launch one instance per module. The pattern I'm using here (don't know if it is the best) is to declare the ProjectResources and setting the launchProfile for a specific value for each. This way I can use Env Variables on the specific launchprofile to tell what modules to load for each instance. This is the way I imagine to "pass data" from the Host to the running instances.

var builder = DistributedApplication.CreateBuilder(args);

var apiGateway = builder.AddProject<Projects.Lynx_Backend_APIGateway>("apigateway");
var db = builder
    .AddSqlServerContainer("dbServer")
    .AddDatabase("db");

// Projects.Lynx_Backend_Host is the host project for every module

var moduleA = builder
    .AddProject<Projects.Lynx_Backend_Host>("Core")
    .WithLaunchProfile("core")
    .WithReference(db);

var moduleB = builder
    .AddProject<Projects.Lynx_Backend_Host>("HR")
    .WithLaunchProfile("hr")
    .WithReference(db);

apiGateway.WithReference(moduleA);
apiGateway.WithReference(moduleB);

builder.Build().Run();

On running this for 2 instances (each one will load a module and run), I get the following error:

 Aspire.Hosting.Dashboard.ProjectViewModelCache[0]
      Task to write view model change terminated for resource type: ProjectViewModel
      System.InvalidOperationException: Sequence contains more than one matching element
         at System.Linq.ThrowHelper.ThrowMoreThanOneMatchException()
         at System.Linq.Enumerable.TryGetSingle[TSource](IEnumerable`1 source, Func`2 predicate, Boolean& found)
         at System.Linq.Enumerable.SingleOrDefault[TSource](IEnumerable`1 source, Func`2 predicate)
         at Aspire.Hosting.ApplicationModel.ProjectResourceExtensions.TryGetProjectWithPath(DistributedApplicationModel model, String path, ProjectResource& projectResource) in /_/src/Aspire.Hosting/ApplicationModel/ProjectResourceExtensions.cs:line 32
         at Aspire.Hosting.Dashboard.ViewModelCache`2.<>c__DisplayClass12_0.<FillEndpoints>b__1(Endpoint ep) in /_/src/Aspire.Hosting/Dashboard/ViewModelCache.cs:line 186
         at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
         at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
         at System.Collections.Generic.List`1.AddRange(IEnumerable`1 collection)
         at Aspire.Hosting.Dashboard.ViewModelCache`2.FillEndpoints(DistributedApplicationModel applicationModel, IEnumerable`1 services, IEnumerable`1 endpoints, CustomResource resource, ResourceViewModel resourceViewModel) in /_/src/Aspire.Hosting/Dashboard/ViewModelCache.cs:line 174
         at Aspire.Hosting.Dashboard.ProjectViewModelCache.ConvertToViewModel(DistributedApplicationModel applicationModel, IEnumerable`1 services, IEnumerable`1 endpoints, Executable executable, List`1 additionalEnvVars) in /_/src/Aspire.Hosting/Dashboard/ProjectViewModelCache.cs:line 40
         at Aspire.Hosting.Dashboard.ViewModelCache`2.ViewModelGeneratingEnumerator.ComputeResult(ObjectChangeType objectChangeType, TResource resource, List`1 additionalEnvVars) in /_/src/Aspire.Hosting/Dashboard/ViewModelCache.cs:line 462
         at Aspire.Hosting.Dashboard.ViewModelCache`2.ViewModelGeneratingEnumerator.MoveNextAsync() in /_/src/Aspire.Hosting/Dashboard/ViewModelCache.cs:line 352
         at Aspire.Hosting.Dashboard.ViewModelCache`2.<>c__DisplayClass7_0.<<-ctor>b__0>d.MoveNext() in /_/src/Aspire.Hosting/Dashboard/ViewModelCache.cs:line 59

Checking the source code I can see that this maybe not going to work, because it checks for projects with the "same path", and in my case they all are the same project running - just with different context.

    /// <summary>
    /// Tries to get the project resource with the specified path from the distributed application model.
    /// </summary>
    /// <param name="model">The distributed application model.</param>
    /// <param name="path">The path of the project resource.</param>
    /// <param name="projectResource">When this method returns, contains the project resource with the specified path, if it is found; otherwise, null.</param>
    /// <returns><see langword="true"/> if the project resource with the specified path is found; otherwise, <see langword="false"/>.</returns>
    public static bool TryGetProjectWithPath(this DistributedApplicationModel model, string path, [NotNullWhen(true)] out ProjectResource? projectResource)
    {
        projectResource = model.GetProjectResources().SingleOrDefault(p => p.Annotations.OfType<IServiceMetadata>().FirstOrDefault()?.ProjectPath == path);

        return projectResource is not null;
    }

Is this pattern some thing supported right now? Or in the future?
Maybe I'm thinking something wrong in my approach to this, does anyone with the same type of solution architecture that has solved this?

Thanks.

[davidfowl]

That approach looks reasonable to be. Given that you do want to model launching the same code as different services. We just have a bug in this TryGetProjectWithPath implementation that assumes there would only be one project with this path. We should be able to solve this.

[davidfowl]

What does “pass configuration” look like?

[antunesl]

For me it's a json, where I can declare all modules being loaded by that "project resource". Each one can run and load 1 or more modules (a module is just a class lib).
Without aspire, I run the Host project that reads a json and do the appropriate, but with Aspire the ideal use case was to be able to "pass some context" to each project resource. Maybe some custom env variable with the json is generic enough to pass some data, this way the configuration stays on the host for flexibility (this is important for deployment).

var moduleA = builder
    .AddProject<Projects.Lynx_Backend_Host>("Core")
    .WithEnvironmentVariable("HOST_CONFIG", "{...}")
    .WithReference(db);

[antunesl]

We should be able to solve this.

Should I open a issue with this?

[davidfowl]

Yep.

[siby-george]

Linking the issue #1072 with fix

[raffaeler]

How can you show a custom name in the dashboard for each instance of the same project?

[davidfowl]

What is a custom name? The resource name isn't the same as the project name.

[raffaeler]

Having multiple instances of the same project, it's more convenient to assign a friendly name to the instance rather then seeing multiple times the same project. This way, you can distinguish the instances.

[davidfowl]

The names have to be distinguished because the resource name cannot be the same.

[raffaeler]

My fault, I gave long names and appeared equal on the dashboard, therefore I was asking how to change the source instead.
Thanks