LOCALSTACK_HOST environment variable mismatch with container port prevents connectivity

[mity1982]

🐛 Bug Description

What happened?
When the connection string is produced, it includes the LocalStack URL as visible from the host machine (e.g., localhost:4567). However, inside the container, only port 4566 is accessible. If the connection string uses a different port (like 4567), components inside the container such as awslocal or health checks cannot connect to LocalStack.

The environment variable LOCALSTACK_HOST is injected/reused in the container and in health checks for connectivity. In my setup, I pin LocalStack's host port to 4567 by setting the container's Port configuration. This results in LOCALSTACK_HOST=localhost:4567, but it should be localhost:4566 for internal container connections.

See the relevant code for context:

dotnet-aspire-for-localstack/src/Aspire.Hosting.LocalStack/Internal/LocalStackConnectionStringAvailableCallback.cs

Line 42 in b7fa6c8

resourceBuilder.WithEnvironment("LOCALSTACK_HOST", $"{localStackUrl.Host}:{localStackUrl.Port.ToString(CultureInfo.InvariantCulture)}");

What did you expect to happen?
LOCALSTACK_HOST inside the container should always reference localhost:4566, regardless of the externally pinned host port. This ensures connectivity for awslocal and health checks.

🔄 Steps to Reproduce

1. Configure LocalStack container with Port=4567 (or any port != 4566).
2. Check injected LOCALSTACK_HOST environment variable inside container.
3. Attempt to use awslocal or health checks within the container.
4. Observe failed connectivity.

Minimal code example:

var builder = DistributedApplication.CreateBuilder(args);
var localstack = builder.AddLocalStack(configureContainer: options => {
    options.Port = 4567;
});
// Components relying on LOCALSTACK_HOST inside container fail
builder.Build().Run();

📋 Environment Information

.NET Aspire Information:

• Aspire Version: 13

LocalStack Information:

• LocalStack Image: 4.13.1

.NET Information:

• .NET Version: 8

Aspire Configuration (Optional):

{
  "LocalStack": {
    "UseLocalStack": true,
  }
}

Error Messages/Stack Traces:

Connection failed: awslocal could not reach localhost:4567 from inside container
Health check failed inside container

[mity1982]

hotfix:

var builder = DistributedApplication.CreateBuilder(args);
var localstack = builder.AddLocalStack(configureContainer: options => {
    options.Port = 4567;
});
localstack.OnConnectionStringAvailable(async (localStackResource, connectionString, ct) =>
{
    localstack .WithEnvironment("LOCALSTACK_HOST", "localhost:4566");
    
    await Task.CompletedTask;
});

builder.Build().Run();

[Blind-Striker]

Hey @mity1982, thanks for the report. I'll look into it