Aspire

// AppHost/Program.csvar builder = DistributedApplication.CreateBuilder(args);
// Infrastructure resourcesvar postgres = builder.AddPostgres("postgres")    .WithPgAdmin()    .AddDatabase("myappdb");
var redis = builder.AddRedis("redis")    .WithRedisInsight();
var rabbitmq = builder.AddRabbitMQ("messaging")    .WithManagementPlugin();
// Application projectsvar api = builder.AddProject<Projects.MyApp_Api>("api")    .WithReference(postgres)    .WithReference(redis)    .WithReference(rabbitmq)    .WithExternalHttpEndpoints();
var worker = builder.AddProject<Projects.MyApp_Worker>("worker")    .WithReference(postgres)    .WithReference(rabbitmq);
builder.Build().Run();

// ServiceDefaults/Extensions.cs — Standard Aspire service defaults// Configures OpenTelemetry (metrics + tracing), health checks, service discovery, and resiliencepublic static class Extensions{    public static IHostApplicationBuilder AddServiceDefaults(this IHostApplicationBuilder builder)    {        builder.ConfigureOpenTelemetry();        builder.AddDefaultHealthChecks();        builder.Services.AddServiceDiscovery();
        builder.Services.ConfigureHttpClientDefaults(http =>        {            http.AddStandardResilienceHandler();            http.AddServiceDiscovery();        });
        return builder;    }
    // ConfigureOpenTelemetry: adds logging, metrics (ASP.NET, HttpClient, Runtime),    //   tracing (ASP.NET, HttpClient, EF Core), and OTLP exporter if configured    // AddDefaultHealthChecks: adds a "self" liveness check tagged ["live"]}

// MyApp.Api/Program.csvar builder = WebApplication.CreateBuilder(args);builder.AddServiceDefaults();
// Add Aspire integrationsbuilder.AddNpgsqlDbContext<AppDbContext>("myappdb");builder.AddRedisDistributedCache("redis");
var app = builder.Build();app.MapDefaultEndpoints(); // health check endpointsapp.Run();

// AppHost — configure service referencesvar orderApi = builder.AddProject<Projects.OrderApi>("order-api");var paymentApi = builder.AddProject<Projects.PaymentApi>("payment-api")    .WithReference(orderApi); // paymentApi can discover orderApi
// In PaymentApi — use service discoverybuilder.Services.AddHttpClient<OrderClient>(client =>{    client.BaseAddress = new Uri("https+http://order-api");});

// BAD — running the AppHost executable in production as an orchestrator// The AppHost is a dev/build-time tool, not a production runtime
// GOOD — deploy the generated assets, not the AppHost://   aspire publish  → docker-compose / Kubernetes manifests from the app model//   aspire deploy   → direct deployment (e.g., Azure Container Apps)

// BAD — hardcoding connection strings defeats Aspire's purposebuilder.Services.AddDbContext<AppDbContext>(o =>    o.UseNpgsql("Host=localhost;Database=myapp;..."));
// GOOD — use Aspire integration (connection string injected automatically)builder.AddNpgsqlDbContext<AppDbContext>("myappdb");

// BAD — manually configuring each servicebuilder.Services.AddOpenTelemetry()...builder.Services.AddHealthChecks()...
// GOOD — use shared service defaultsbuilder.AddServiceDefaults();