What is the AppHost?

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Aspire’s AppHost is the code-first place where you declare your application’s services and their relationships. Instead of managing scattered configuration files, you describe the architecture in code. Aspire then handles local orchestration so you can focus on building features.

Defining your architecture

Consider a simple three-tier architecture where a frontend talks to an API, and the API relies on a database. Select an API language below to see the examples demonstrated in that language.

Select your API platform

architecture-beta

  service db(logos:postgresql)[PostgreSQL]
  service api(logos:dotnet)[API service]
  service frontend(logos:react)[React frontend]

  api:R --> L:db
  frontend:R --> L:api

This architecture demonstrates a .NET API connecting to a PostgreSQL database, with a React frontend consuming the API. The .NET API uses ASP.NET Core and connects to PostgreSQL using Entity Framework or a connection string. The React frontend is built with Vite and communicates with the API over HTTP.

To build this architecture step-by-step, see the Build your first app quickstart.

architecture-beta

  service db(logos:postgresql)[PostgreSQL]
  service api(logos:python)[API service]
  service frontend(logos:react)[React frontend]

  api:R --> L:db
  frontend:R --> L:api

This architecture demonstrates a Python API (using FastAPI/Uvicorn) connecting to a PostgreSQL database, with a React frontend consuming the API. The Python API uses frameworks like FastAPI or Flask and connects to PostgreSQL using libraries like psycopg2 or SQLAlchemy. The React frontend is built with Vite and communicates with the API over HTTP.

To add this architecture to an existing Python-backed app, start with Add Aspire to an existing app and then review the Python integration.

architecture-beta

  service db(logos:postgresql)[PostgreSQL]
  service api(logos:nodejs-icon)[API service]
  service frontend(logos:react)[React frontend]

  api:R --> L:db
  frontend:R --> L:api

This architecture demonstrates a Node.js API connecting to a PostgreSQL database, with a React frontend consuming the API. The Node.js API uses frameworks like Express or Fastify and connects to PostgreSQL using libraries like pg or Prisma. The React frontend is built with Vite and communicates with the API over HTTP.

architecture-beta

  service db(logos:postgresql)[PostgreSQL]
  service api(logos:go)[API service]
  service frontend(logos:react)[React frontend]

  api:R --> L:db
  frontend:R --> L:api

This architecture demonstrates a Go API connecting to a PostgreSQL database, with a React frontend consuming the API. The Go API uses the standard library’s net/http package or frameworks like Gin or Echo and connects to PostgreSQL using libraries like pgx or database/sql. The React frontend is built with Vite and communicates with the API over HTTP.

architecture-beta

  service db(logos:postgresql)[PostgreSQL]
  service api(logos:java)[API service]
  service frontend(logos:react)[React frontend]

  api:R --> L:db
  frontend:R --> L:api

This architecture demonstrates a Java API (using Spring Boot) connecting to a PostgreSQL database, with a React frontend consuming the API. The Java API uses Spring Boot with Spring Data JPA and connects to PostgreSQL using JDBC or Spring Data. The React frontend is built with Vite and communicates with the API over HTTP.

You can represent that architecture in an AppHost like this:

C# AppHost
TypeScript AppHost

var builder = DistributedApplication.CreateBuilder(args);

// Add database resource
var postgres = builder.AddPostgres("db")
    .AddDatabase("appdata")
    .WithDataVolume();

// Add API service and reference the database
var api = builder.AddProject<Projects.Api>("api")
    .WithReference(postgres)
    .WaitFor(postgres);

// Add frontend service and reference the API
builder.AddViteApp("frontend", "../frontend")
    .WithHttpEndpoint(env: "PORT")
    .WithReference(api);

builder.Build().Run();

Uses AddProject<Projects.Api>() to reference a .NET project.

import { createBuilder } from './.modules/aspire.js';

const builder = await createBuilder();

// Add database resource
const postgres = await builder.addPostgres("db")
    .addDatabase("appdata")
    .withDataVolume();

// Add API service and reference the database
const api = await builder.addProject("api", "../api/Api.csproj", "https")
    .withReference(postgres)
    .waitFor(postgres);

// Add frontend service and reference the API
await builder.addViteApp("frontend", "../frontend")
    .withHttpEndpoint({ env: "PORT" })
    .withReference(api);

await builder.build().run();

Uses addProject() to reference the API project.

C# AppHost
TypeScript AppHost

var builder = DistributedApplication.CreateBuilder(args);

// Add database resource
var postgres = builder.AddPostgres("db")
    .AddDatabase("appdata")
    .WithDataVolume();

// Add API service and reference the database
var api = builder.AddUvicornApp("api", "../api", "main:app")
    .WithUv()
    .WithReference(postgres)
    .WaitFor(postgres);

// Add frontend service and reference the API
builder.AddViteApp("frontend", "../frontend")
    .WithHttpEndpoint(env: "PORT")
    .WithReference(api);

builder.Build().Run();

Uses AddUvicornApp() with WithUv() for ASGI apps like FastAPI.

import { createBuilder } from './.modules/aspire.js';

const builder = await createBuilder();

// Add database resource
const postgres = await builder.addPostgres("db")
    .addDatabase("appdata")
    .withDataVolume();

// Add API service and reference the database
const api = await builder.addUvicornApp("api", "../api", "main:app")
    .withUv()
    .withReference(postgres)
    .waitFor(postgres);

// Add frontend service and reference the API
await builder.addViteApp("frontend", "../frontend")
    .withHttpEndpoint({ env: "PORT" })
    .withReference(api);

await builder.build().run();

Uses addUvicornApp() with withUv() for ASGI apps like FastAPI.

C# AppHost
TypeScript AppHost

var builder = DistributedApplication.CreateBuilder(args);

// Add database resource
var postgres = builder.AddPostgres("db")
    .AddDatabase("appdata")
    .WithDataVolume();

// Add API service and reference the database
var api = builder.AddNodeApp("api", "../api", "server.js")
    .WithNpm()
    .WithReference(postgres)
    .WaitFor(postgres);

// Add frontend service and reference the API
builder.AddViteApp("frontend", "../frontend")
    .WithHttpEndpoint(env: "PORT")
    .WithReference(api);

builder.Build().Run();

Uses AddNodeApp() with WithNpm() for Node.js applications.

import { createBuilder } from './.modules/aspire.js';

const builder = await createBuilder();

// Add database resource
const postgres = await builder.addPostgres("db")
    .addDatabase("appdata")
    .withDataVolume();

// Add API service and reference the database
const api = await builder.addNodeApp("api", "../api", "server.js")
    .withNpm()
    .withReference(postgres)
    .waitFor(postgres);

// Add frontend service and reference the API
await builder.addViteApp("frontend", "../frontend")
    .withHttpEndpoint({ env: "PORT" })
    .withReference(api);

await builder.build().run();

Uses addNodeApp() with withNpm() for Node.js applications.

var builder = DistributedApplication.CreateBuilder(args);

// Add database resource
var postgres = builder.AddPostgres("db")
    .AddDatabase("appdata")
    .WithDataVolume();

// Add API service and reference the database
var api = builder.AddGolangApp("api", "../api")
    .WithHttpEndpoint(env: "PORT")
    .WithReference(postgres)
    .WaitFor(postgres);

// Add frontend service and reference the API
builder.AddViteApp("frontend", "../frontend")
    .WithHttpEndpoint(env: "PORT")
    .WithReference(api);

builder.Build().Run();

Uses AddGolangApp() for Go applications.

var builder = DistributedApplication.CreateBuilder(args);

// Add database resource
var postgres = builder.AddPostgres("db")
    .AddDatabase("appdata")
    .WithDataVolume();

// Add API service and reference the database
var api = builder.AddSpringApp("api", "../api", "otel.jar")
    .WithHttpEndpoint(port: 8080)
    .WithReference(postgres)
    .WaitFor(postgres);

// Add frontend service and reference the API
builder.AddViteApp("frontend", "../frontend")
    .WithHttpEndpoint(env: "PORT")
    .WithReference(api);

builder.Build().Run();

Uses AddSpringApp() for Spring Boot applications.

The AppHost models your distributed application declaratively. Each code sample above shows the same three-tier architecture—PostgreSQL database, API service, and React frontend—but with different API implementations and, when available, different AppHost languages.

In all cases, the PostgreSQL database and React frontend remain identical. Aspire resource references establish dependencies between resources, and the app model ensures services start in the correct order.

Aspire presents the same, consistent model regardless of the language or framework used: services, resources, and the connections between them.