.NET Aspire emerged alongside .NET 8 and C# 12 as a surprise addition that quickly gained traction by tackling a long-standing pain point: developing and debugging distributed applications locally with ease. This chapter introduces the motivation behind Aspire, explains the book’s goal of teaching its core principles, and orients readers new to distributed systems. It sets the stage by contrasting distributed architectures with monoliths and frames how Aspire streamlines running complex, multi-service solutions in a consistent way across development and production.
The chapter provides a high-level tour of distributed systems and orchestration: what distributed applications are, why teams adopt them, and the trade-offs they introduce. It outlines orchestration responsibilities—deployment, scaling, health checks, configuration, load balancing, and resource allocation—and shows how Aspire addresses these needs. Aspire offers a cloud-native application stack that declutters microservice development through a declarative model for services and dependencies, unified local orchestration, strong observability via OpenTelemetry, and out-of-the-box integration with common infrastructure such as databases and message brokers. The result is faster iteration, clearer service boundaries, and an easier path from local development to cloud deployment.
Practically, the chapter walks through the Starter Project structure: a Blazor frontend, an API service, an AppHost orchestrator, and a ServiceDefaults library. It demonstrates registering projects with the host, exposing only necessary external endpoints, coordinating startup with dependency readiness, and enabling service discovery so clients communicate by service name (e.g., resolving “apiservice”) rather than fixed addresses. ServiceDefaults provides extension methods that standardize telemetry, health checks, HTTP client resilience, and discovery across services. With its dashboard for endpoints, logs, and status, Aspire makes multi-service apps runnable and debuggable in one place, preparing readers to extend these foundations and dive deeper into monitoring in the next chapter.
Example of a distributed application
Modular monolith structure
Orchestrated system
Hosting code and infrastructure components in the same Aspire process
The structure of the Aspire solution
Aspire dashboard
Aspire console log
Aspire Resources webfrontend link
Blazor app hosted in Aspire
Summary
.NET Aspire was created by Microsoft to make the process of developing distributed applications easy.
Distributed applications are systems that consist of multiple independent services that interact with each other.
Orchestration is the process of coordinating services inside a distributed system
The main benefit of using .NET Aspire is that it allows running and debugging a distributed application in a single process on a development machine, which substantially simplifies the development process
.NET Aspire consists of the Aspire Host project that all other projects can connect to
Different applications hosted by .NET Aspire can pass each other’s references to each other when they are registered by the orchestrator
The Service Defaults project is used for shared dependencies that any Aspire-hosted apps can use
Service discovery allows to resolve addresses of Aspire-hosted apps via the names the apps were registered under in the orchestrator
Aspire orchestrator displays a dashboard, which shows the status of all running services
FAQ
What is .NET Aspire and why did it gain attention?.NET Aspire is a cloud-native application stack that simplifies building, running, and monitoring distributed .NET applications. Released alongside .NET 8/C# 12, it stood out by enabling developers to run entire multi-service systems locally in a single orchestrated process with first-class debugging and observability.How does a distributed application differ from a monolithic (or modular monolith) application?A distributed app is composed of autonomous services, each running in its own process and communicating over lightweight mechanisms (often HTTP). They can be developed, deployed, and scaled independently. A monolith bundles all business logic into a single executable (even if modular internally), so deployment and scaling are done as one unit.What challenges of distributed systems does .NET Aspire help mitigate?It reduces development and operational friction by: running multiple services together locally, simplifying orchestration, enabling service discovery, providing health checks and telemetry out of the box, and making it easier to debug and observe services as a cohesive system.What does orchestration mean in this context?Orchestration coordinates services so they work together, handling deployment, scaling, load balancing, health monitoring/self-healing, configuration management (including secrets), and resource allocation. Aspire acts as an orchestrator during development.What is included in the Aspire Starter Project template?The template typically creates: a Blazor UI app (AspireApp.Web), an API service (AspireApp.ApiService), an Aspire host/orchestrator (AspireApp.AppHost), and a shared class library for service defaults (AspireApp.ServiceDefaults).How do I run and inspect an Aspire solution?Start the host project (e.g., AspireApp.AppHost). Aspire builds and launches all registered services and shows a dashboard with service states, endpoints, logs, and details. You can open service endpoints directly from the dashboard.How are applications registered with the Aspire host?In the host’s startup (Program.cs or AppHost.cs), use the distributed app builder: AddProject for each service, optionally WithExternalHttpEndpoints for public exposure, WithReference to declare dependencies, and WaitFor to control startup order. Example: builder.AddProject<Projects.AspireApp_Web>("webfrontend").WithExternalHttpEndpoints().WaitFor(apiService).WithReference(apiService);What are “Service Defaults” and why are they important?Service Defaults are extension methods in a shared library that standardize cross-cutting concerns: service discovery, health checks, telemetry (OpenTelemetry), HTTP client defaults, and resilience. They’re included so teams can customize them for their scenario.How do I enable and use service discovery in .NET Aspire?Install Microsoft.Extensions.ServiceDiscovery (typically via the ServiceDefaults project) and register it in AddServiceDefaults(). Then resolve services by name using the Aspire-aware URI scheme. Example: client.BaseAddress = new("https+http://apiservice"); Aspire resolves the correct address at runtime.How does Aspire handle service exposure and security of endpoints?By default, services are reachable only on Aspire’s internal network. Expose a service publicly by calling WithExternalHttpEndpoints() for that project (e.g., the UI). Keep backend services (like APIs) internal, and let other services reach them via service discovery.
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