Passing Aspire-Configured RabbitMQ Credentials to Environment Variables

[sharpzilla]

I have a Microsoft.NET.Sdk.Worker project where I use ConfigurationBuilder for configuring my services:

ConfigurationBuilder()
    .SetBasePath(AppContext.BaseDirectory)
    .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
    .AddEnvironmentVariables()
    .Build();

For working with RabbitMQ, I have a wrapper around EasyNetQ. In the DI of this wrapper service, I pass a strongly-typed object whose values are taken from the appsettings.json file:

"RabbitMQConfig": {
    "username": "username",
    "password": "password",
    "host": "localhost"
}

Now I have configured RabbitMQ in the Aspire project:

var rabbitMq = builder.AddRabbitMQ("messaging")
    .WithImageTag("4.0.5-management")
    .WithManagementPlugin();

var workerProject = builder.AddProject<Worker>("worker")
    .WithReference(rabbitMq)
    .WaitFor(rabbitMq);

builder.Build().Run();

How can I pass the username and password configured by Aspire for RabbitMQ into environment variables for the Worker project in the RabbitMQConfig:username and RabbitMQConfig:password sections? If I understand correctly, since AddEnvironmentVariables is called after AddJsonFile, the runtime environment variables should override the JSON configuration values.

Currently, my Aspire code works, and it starts the rabbitmq container and the Worker service, but only if I comment out the service registration for working with RabbitMQ in the Worker. Otherwise, the application fails to connect to RabbitMQ.

[davidfowl]

When you use WithReference, we pass connection information to the target resource (a project in your example). Each of the integration has the documented connection format for each resource. For RabbitMQ:
https://learn.microsoft.com/en-us/dotnet/aspire/messaging/rabbitmq-integration?tabs=dotnet-cli#use-a-connection-string

On top of that, each resource has an object model with various properties:

https://learn.microsoft.com/en-us/dotnet/api/aspire.hosting.applicationmodel.rabbitmqserverresource?view=dotnet-aspire-8.0#properties

Those properties are used to create the default connection string that is used by WithReference, e.g For RabbitMQServerResource (which is the resource type when you call AddRabbitMQ):

aspire/src/Aspire.Hosting.RabbitMQ/RabbitMQServerResource.cs

Line 53 in 89e329c

public ReferenceExpression ConnectionStringExpression =>

Given that you should be able to something like this in your app host project:

var rabbitMq = builder.AddRabbitMQ("messaging")
    .WithImageTag("4.0.5-management")
    .WithManagementPlugin();

var workerProject = builder.AddProject<Worker>("worker")
    .WithEnvironment(context =>
    {
        context.EnvironmentVariables["RabbitMQConfig__username"] = rabbitMq.Resource.UserNameParameter ?? (object)"guest";
        context.EnvironmentVariables["RabbitMQConfig__password"] = rabbitMq.Resource.PasswordParameter;
        context.EnvironmentVariables["RabbitMQConfig__host"] = rabbitMq.Resource.PrimaryEndpoint.Property(EndpointProperty.Host);
    })
    .WaitFor(rabbitMq);

builder.Build().Run();