Benchmarking Aspire 13.5 Dashboard Terminals for Multi-Replica Services

Introduction

When working with distributed applications, developers usually have several terminals open at the same time.

One terminal runs the API. Another runs a worker. Another shows database logs. If a service has multiple replicas, things become even more confusing because each replica may have its own process and output.

.NET Aspire 13.5 addresses part of this problem by bringing an interactive terminal directly into the Aspire dashboard.

With the new WithTerminal() capability, a resource can expose an interactive terminal session that developers can use from the dashboard. Aspire 13.5 also allows developers to switch between replicas and supports multiple viewers attaching to the same terminal session. The matching aspire terminal CLI commands can be used to list and attach to terminal sessions. These terminal APIs are experimental in Aspire 13.5.

This is particularly interesting for applications that run multiple instances of the same resource.

Instead of:

Terminal 1 → API Replica 1
Terminal 2 → API Replica 2
Terminal 3 → API Replica 3

the developer can work through the Aspire dashboard:

Aspire Dashboard
       |
       v
Orders API
   |
   +---- Replica 1
   +---- Replica 2
   +---- Replica 3
          |
          v
     Interactive Terminal

The feature is not really about replacing terminals. It is about making interactive distributed resources easier to discover, access, and manage.

What Is the Aspire Dashboard Terminal?

Traditional Aspire resources generally expose information through logs and telemetry.

For example:

Orders API
   |
   +--> Console Logs
   +--> Traces
   +--> Metrics

But some applications do not behave like ordinary background services.

They may require:

Standard input
Interactive shells
REPL commands
Terminal-based user interfaces
Interactive debugging tools
Developer utilities

Aspire 13.5 adds a terminal experience for these scenarios.

The AppHost can configure a resource with:

.WithTerminal()

The resource can then be accessed through an interactive terminal in the dashboard. Microsoft describes this as a way to run shells, REPLs, terminal user interfaces, and other applications that expect real stdin and stdout.

Why Interactive Terminals Matter in Distributed Applications

Consider an application with three API replicas:

Orders API
   |
   +--> Replica 1
   +--> Replica 2
   +--> Replica 3

Suppose Replica 2 is behaving differently from the others.

Without an integrated terminal, a developer may need to determine:

Which process?
Which terminal?
Which port?
Which replica?
Which logs?

That creates unnecessary friction.

The Aspire dashboard already knows about the resources and their replicas, so bringing the terminal into the same interface creates a more connected development experience.

The workflow becomes:

Dashboard
   |
   v
Orders API
   |
   v
Select Replica 2
   |
   v
Open Terminal
   |
   v
Investigate

This is particularly useful during local debugging and development.

Understanding Aspire Replicas

Aspire supports running multiple replicas of a resource using the WithReplicas API.

For example:

var builder = DistributedApplication.CreateBuilder(args);

var api = builder.AddProject<Projects.OrdersApi>("orders-api")
                 .WithReplicas(3);

builder.Build().Run();

The exact project type and AppHost structure depend on the application, but the important concept is that Aspire can represent multiple instances of the same logical resource.

The dashboard represents the parent resource and its individual replicas separately. Each replica has its own resource identity and logs.

Conceptually:

orders-api
    |
    +-- orders-api-replica-1
    +-- orders-api-replica-2
    +-- orders-api-replica-3

This gives developers a way to inspect individual instances instead of treating the entire service as one undifferentiated process.

Adding a Terminal to a Resource

The key API introduced for this workflow is:

.WithTerminal()

A simplified AppHost example is:

var builder = DistributedApplication.CreateBuilder(args);

var worker = builder.AddProject<Projects.Worker>("worker")
                    .WithTerminal();

builder.Build().Run();

Once the application starts, the resource can expose an interactive terminal through the Aspire dashboard.

The important thing to understand is that the terminal belongs to the resource's process.

It is not simply another console-log viewer.

A log viewer is generally:

Process
   |
   v
stdout/stderr
   |
   v
Dashboard

An interactive terminal is:

Developer
   |
   v
Dashboard Terminal
   |
   +--> stdin
   |
   +--> Process
   |
   +<-- stdout
   |
   +<-- stderr

That distinction makes the feature useful for applications that actually require interaction.

Terminal vs Console Logs

These two capabilities solve different problems.

Feature	Console Logs	Interactive Terminal
View stdout	Yes	Yes
View stderr	Yes	Yes
Send input	No	Yes
Interactive commands	No	Yes
REPL applications	No	Yes
Terminal UI	No	Yes
Follow process output	Yes	Yes
Switch replicas	Resource-based	Supported
Multiple viewers	Log viewing	Terminal sessions can have multiple viewers

Aspire's dashboard already provides resource logs and telemetry. The terminal extends that experience to applications that require interactive input.

Multi-Replica Terminal Workflow

Now consider a service with three replicas:

orders-api
│
├── replica-1
├── replica-2
└── replica-3

Suppose each replica has an interactive process.

The dashboard can provide a way to switch between replicas:

+--------------------------------+
| Orders API                     |
|                                |
| Replica: [ replica-2       ▼ ] |
|                                |
| > diagnostic command           |
| > status                       |
|                                |
| Process output...              |
+--------------------------------+

This is useful when a problem appears only on one instance.

Instead of opening several terminal windows and manually tracking which process belongs to which replica, the resource hierarchy provides the context.

Microsoft specifically calls out replica switching as part of the 13.5 terminal experience.

Multiple Viewers

Another interesting capability is that multiple viewers can attach to the same terminal session.

For example:

                 Terminal Session
                       |
             +---------+---------+
             |                   |
             v                   v
       Dashboard Tab        Local Terminal

This can be useful during collaborative debugging.

One developer might be looking at the Aspire dashboard while another connects from a local terminal.

The important point is that both can observe the same interactive process rather than creating separate processes simply because they need different access points. Microsoft explicitly describes multiple viewers attaching to a terminal session in Aspire 13.5.

Using the Aspire CLI

The dashboard is not the only way to access these sessions.

Aspire 13.5 also introduces matching terminal commands through the CLI.

Microsoft's release notes describe commands that can list terminal sessions and attach to them. The terminal command feature must be enabled because the terminal APIs are experimental in this release.

Conceptually, the workflow becomes:

aspire terminal list

Then:

aspire terminal attach <session>

The exact command syntax and feature-flag requirements should be checked against the Aspire 13.5 CLI documentation because the terminal functionality is experimental.

This gives developers two access patterns:

Dashboard
   |
   +--> Interactive Terminal

CLI
   |
   +--> Attach to Terminal Session

That flexibility is useful for developers who prefer terminal-first workflows.

Building a Simple Interactive Resource

A good example is a small command-line application.

Imagine a .NET application that asks the developer for a number:

Console.Write("Enter a number: ");

var input = Console.ReadLine();

if (int.TryParse(input, out var number))
{
    Console.WriteLine($"You entered: {number}");
}
else
{
    Console.WriteLine("Invalid number.");
}

Normally, this application expects a real terminal.

If it is modeled as an Aspire resource with terminal support, the developer can interact with it from the Aspire dashboard rather than opening a completely separate terminal window.

That makes it a simple demonstration of why stdin support matters.

A More Realistic Developer Tool

The same concept becomes more useful with a development utility.

For example:

Database Utility

> migrate
> seed
> reset
> status
> exit

The application might contain:

while (true)
{
    Console.Write("> ");

    var command = Console.ReadLine();

    switch (command)
    {
        case "status":
            Console.WriteLine("Database is ready.");
            break;

        case "seed":
            await SeedDatabaseAsync();
            Console.WriteLine("Seed completed.");
            break;

        case "exit":
            return;

        default:
            Console.WriteLine("Unknown command.");
            break;
    }
}

With an interactive terminal, such a tool can become part of the Aspire development environment.

Instead of documenting:

Open another terminal.
Navigate to this directory.
Run this command.
Set this environment variable.

the developer can access the resource directly from Aspire.

Benchmarking the Terminal Experience

The article title uses the word "benchmarking," but this should not be interpreted as a claim that the dashboard terminal is faster than a traditional terminal.

There is no meaningful reason to invent a universal latency benchmark for this feature.

Instead, benchmark the developer workflow.

Useful measurements include:

Measurement	What to Observe
Session startup	How quickly a terminal becomes available
Replica switching	Time required to move between instances
Input responsiveness	Whether commands feel interactive
Output rendering	Whether output remains readable
Reconnection	Behavior after dashboard reconnects
Multiple viewers	Behavior when several clients attach
CLI attach	Ease of moving from dashboard to terminal
Resource discovery	How quickly developers identify the correct replica

These measurements are more useful than simply measuring terminal throughput.

Testing Replica Switching

A useful test setup might use three replicas:

var api = builder.AddProject<Projects.OrdersApi>("orders-api")
                 .WithReplicas(3)
                 .WithTerminal();

Then verify:

Replica 1
   |
   +--> Terminal opens
   +--> Input works
   +--> Output visible

Replica 2
   |
   +--> Terminal opens
   +--> Input works
   +--> Output visible

Replica 3
   |
   +--> Terminal opens
   +--> Input works
   +--> Output visible

The goal is not to prove that all replicas are identical.

It is to verify that the developer can reliably identify and interact with the intended instance.

Why Replica-Specific Debugging Matters

Distributed applications often behave differently across instances.

For example:

Replica 1 → Healthy
Replica 2 → Slow
Replica 3 → Healthy

The cause could be:

Different startup state
Temporary external dependency failure
Replica-specific data
Configuration differences
Resource pressure
A timing-related problem

A centralized dashboard with replica-aware terminal access makes the debugging workflow more direct.

The developer can:

Identify replica
      ↓
Open terminal
      ↓
Inspect state
      ↓
Run diagnostic command
      ↓
Compare with another replica

Terminal Sessions and Resource Identity

One important design principle is to keep the resource identity clear.

Suppose the dashboard shows:

payments-api

and:

payments-api-abc123
payments-api-def456
payments-api-ghi789

A developer should be able to understand that the child entries represent individual replicas.

Aspire's dashboard already uses this model for resource logs and telemetry. Replicated resources are represented under a parent resource with individual replica entries.

This same mental model makes terminal access easier to understand.

Terminal Sessions Are Not Debuggers

Another important distinction is that an interactive terminal is not the same thing as an IDE debugger.

Aspire 13.5's release notes explicitly state that resources using the terminal currently run as plain processes, so developers should attach the debugger manually when debugging is required.

Therefore:

Terminal
   |
   +--> stdin/stdout interaction
   +--> commands
   +--> REPL
   +--> diagnostics

is different from:

Debugger
   |
   +--> Breakpoints
   +--> Step Into
   +--> Step Over
   +--> Variables
   +--> Call Stack

Do not expect WithTerminal() to replace your normal debugger.

Common Mistakes

Mistake 1: Treating the Terminal as a Log Viewer

A terminal exists for interactive input and output.

If the application only produces logs, the standard dashboard console is usually enough.

Mistake 2: Assuming Every Resource Needs a Terminal

Adding terminal support to every resource can make the development environment harder to understand.

Use it where interactive behavior provides real value.

Mistake 3: Expecting Debugger Integration

The terminal is not a replacement for Visual Studio, VS Code, or another debugger. Aspire 13.5 currently requires manual debugger attachment for terminal resources.

Mistake 4: Ignoring Replica Identity

When debugging multiple replicas, always verify which instance you are interacting with.

Mistake 5: Treating Experimental APIs as Stable

WithTerminal() and the corresponding CLI commands are experimental in Aspire 13.5.

Troubleshooting

Problem	What to Check
Terminal does not appear	Verify .WithTerminal() is configured
Input does not work	Confirm the application actually reads stdin
Wrong replica selected	Check the resource hierarchy
Terminal disconnects	Check dashboard/session state
CLI attach unavailable	Verify the terminal CLI feature is enabled
Debugging does not work	Attach the debugger manually
Multiple viewers behave unexpectedly	Verify the terminal session and viewer configuration
Resource behaves differently per replica	Inspect each replica individually

Advantages

One Place for Distributed Development

The dashboard becomes a central place for resources, logs, telemetry, and interactive terminals.

Easier Replica Debugging

Developers can move between replicas without manually tracking multiple terminal windows.

Better Developer Experience

Interactive applications become easier to discover and use.

Multiple Viewer Support

More than one client can observe the same terminal session, which can help during collaborative troubleshooting.

Dashboard and CLI Access

Developers can choose between the graphical dashboard and terminal-based workflow.

Disadvantages and Limitations

Experimental API

The terminal APIs are experimental in Aspire 13.5, so teams should expect changes as the feature evolves.

Not a Debugger

Developers still need normal debugger tooling for breakpoints and step-through debugging.

Not Necessary for Every Service

Most standard web APIs do not need interactive stdin.

More Resource Complexity

Adding interactive capabilities can make an AppHost more complex if used without a clear reason.

Workflow Still Needs Validation

Teams should test reconnection, replica selection, and multi-viewer behavior before depending heavily on the feature.

Best Practices

Use Terminals for Truly Interactive Resources

Good candidates include:

REPL applications
CLI tools
Terminal UIs
Interactive workers
Development utilities
Shell-based diagnostics

Keep Standard Services Simple

If an API only produces logs and telemetry, use the existing Aspire dashboard features.

Make Replica Identity Obvious

When multiple replicas exist, make sure developers can easily determine which instance they are interacting with.

Keep Debugging Tools Separate

Use the terminal for interaction and the debugger for debugging.

Test the Workflow With Multiple Replicas

Do not assume single-replica behavior represents a multi-replica environment.

Be Careful With Experimental Features

Because terminal support is experimental in 13.5, isolate usage behind a clear development strategy and be prepared for API changes.

A Practical Multi-Replica Example

A simple AppHost could look like:

var builder = DistributedApplication.CreateBuilder(args);

var api = builder.AddProject<Projects.OrdersApi>("orders-api")
                 .WithReplicas(3)
                 .WithTerminal();

var worker = builder.AddProject<Projects.OrderWorker>("order-worker")
                    .WithTerminal();

builder.Build().Run();

The resulting development environment could conceptually look like:

Aspire Dashboard
│
├── orders-api
│   ├── replica-1
│   │   └── Terminal
│   ├── replica-2
│   │   └── Terminal
│   └── replica-3
│       └── Terminal
│
└── order-worker
    └── Terminal

This is where the feature starts to become genuinely useful.

The dashboard is no longer only showing the distributed system. It becomes an interactive control surface for development resources.

Conclusion

Aspire 13.5's dashboard terminal is a useful improvement for developers working with interactive processes and multiple replicas. The biggest benefit is not that it eliminates the normal terminal, but that it brings interactive resources into the same place where developers already see their services, logs, and telemetry. Being able to switch between replicas and have multiple viewers attach to a session can make certain debugging and development workflows much easier to manage. At the same time, the feature is still experimental, and it should not be treated as a replacement for a proper debugger or as something every resource needs. For teams building distributed .NET applications with CLI tools, REPLs, terminal-based utilities, or replica-specific troubleshooting needs, WithTerminal() is worth experimenting with and evaluating as part of the local development experience.