Configuration

Cratis Arc can be configured both through appsettings.json and programmatically to customize its behavior. The main configuration is handled through the ArcOptions class.

This page covers the ASP.NET Core host specifically. For the lightweight Arc.Core host and its listen URL configuration, see Arc.Core Getting Started.

Default Configuration Section

By default, Arc looks for configuration under the Cratis:Arc section in your appsettings.json file. The same keys can be supplied through environment variables — .NET maps the __ separator onto nested keys, so Cratis:Arc:GeneratedApis:RoutePrefix becomes Cratis__Arc__GeneratedApis__RoutePrefix.

Configuration Options

Configuration example

Here’s an example covering the most common options, bound from appsettings.json under Cratis:Arc:

{
  "Cratis": {
    "Arc": {
      "CorrelationId": {
        "HttpHeader": "X-Correlation-ID"
      },
      "Tenancy": {
        "ResolverType": "Header",
        "HttpHeader": "x-cratis-tenant-id"
      },
      "GeneratedApis": {
        "RoutePrefix": "api",
        "SegmentsToSkipForRoute": 0,
        "IncludeCommandNameInRoute": true,
        "IncludeQueryNameInRoute": true
      },
      "Query": {
        "KeepAliveInterval": "00:00:30"
      }
    }
  }
}

Note

ArcOptions.Hosting (the listen URL) applies only to Arc.Core hosts — in an ASP.NET Core app the URL comes from Kestrel and launchSettings.json, not from Arc. For the Arc.Core hosting shape, see Arc.Core Getting Started.

Configuration Properties

CorrelationId

Controls how correlation IDs are handled in HTTP requests.

• HttpHeader (string, default: "X-Correlation-ID"): The HTTP header name to use for correlation ID tracking.

Tenancy

Controls how the active tenant is resolved on each request.

• ResolverType (TenantResolverType, default: Header): How to resolve the tenant — Header, Query, Claim, or Development.
• HttpHeader (string, default: "x-cratis-tenant-id"): The HTTP header used when ResolverType is Header.
• QueryParameter (string, default: "tenantId"): The query-string parameter used when ResolverType is Query.
• ClaimType (string, default: "tenant_id"): The claim used when ResolverType is Claim.
• DevelopmentTenantId (string, default: "development"): The fixed tenant used when ResolverType is Development.

GeneratedApis

Controls how automatically generated API endpoints are configured for commands and queries.

• RoutePrefix (string, default: "api"): The base route prefix for all generated API endpoints.
• SegmentsToSkipForRoute (int, default: 0): Number of namespace segments to skip when constructing routes from type namespaces.
• IncludeCommandNameInRoute (bool, default: true): Whether to include the command type name as the last segment of the route for command endpoints.
• IncludeQueryNameInRoute (bool, default: true): Whether to include the query type name as the last segment of the route for query endpoints.

Query

Controls observable (real-time) queries.

• KeepAliveInterval (TimeSpan, default: 00:00:30): How often a keep-alive frame is sent on an open observable-query connection.

IdentityDetailsProvider

• IdentityDetailsProvider (Type, default: null): Specifies a custom identity details provider type. If not specified, the system will use type discovery to find one automatically.

Setup Methods

The ASP.NET Core host bootstraps with WebApplication.CreateBuilder, registers Arc with AddCratisArc, and activates it with UseCratisArc.

Using Configuration File

The most common approach is to use the configuration file with the default section:

var builder = WebApplication.CreateBuilder(args);

// Bind the default configuration section (Cratis:Arc)
builder.AddCratisArc();

var app = builder.Build();
app.UseCratisArc();
app.Run();

Using Custom Configuration Section

You can specify a custom configuration section path:

var builder = WebApplication.CreateBuilder(args);

// Bind a custom configuration section
builder.AddCratisArc(configSectionPath: "MyApp:CratisConfig");

var app = builder.Build();
app.UseCratisArc();
app.Run();

Programmatic Configuration

You can configure the options through code with the configureOptions callback:

var builder = WebApplication.CreateBuilder(args);

builder.AddCratisArc(options =>
{
    // Configure correlation ID
    options.CorrelationId.HttpHeader = "X-My-Correlation-ID";

    // Configure tenancy
    options.Tenancy.HttpHeader = "X-Tenant-ID";

    // Configure generated APIs
    options.GeneratedApis.RoutePrefix = "myapi";
    options.GeneratedApis.SegmentsToSkipForRoute = 2;
    options.GeneratedApis.IncludeCommandNameInRoute = false;
    options.GeneratedApis.IncludeQueryNameInRoute = false;

    // Set a custom identity details provider
    options.IdentityDetailsProvider = typeof(MyCustomIdentityDetailsProvider);
});

var app = builder.Build();
app.UseCratisArc();
app.Run();

Hybrid Configuration

AddCratisArc binds appsettings.json first and then applies the configureOptions callback, so the callback acts as a programmatic override on top of file-based settings:

var builder = WebApplication.CreateBuilder(args);

// Values come from Cratis:Arc; the callback overrides specific settings
builder.AddCratisArc(options =>
{
    options.GeneratedApis.RoutePrefix = "v1/api";
});

var app = builder.Build();
app.UseCratisArc();
app.Run();

Environment-Specific Configuration

You can use different configurations for different environments using the standard ASP.NET Core configuration pattern:

appsettings.json (base configuration):

{
  "Cratis": {
    "Arc": {
      "GeneratedApis": {
        "RoutePrefix": "api"
      }
    }
  }
}

appsettings.Development.json (development overrides):

{
  "Cratis": {
    "Arc": {
      "CorrelationId": {
        "HttpHeader": "X-Dev-Correlation-ID"
      }
    }
  }
}

appsettings.Production.json (production overrides):

{
  "Cratis": {
    "Arc": {
      "GeneratedApis": {
        "RoutePrefix": "v1"
      }
    }
  }
}

Route Generation Examples

The GeneratedApis configuration affects how routes are generated for your commands and queries. Here are some examples:

Given a command class MyApp.Sales.Commands.CreateOrderCommand:

Default Configuration

{
  "GeneratedApis": {
    "RoutePrefix": "api",
    "SegmentsToSkipForRoute": 0,
    "IncludeCommandNameInRoute": true,
    "IncludeQueryNameInRoute": true
  }
}

Generated route: /api/MyApp/Sales/Commands/CreateOrderCommand

Skip Namespace Segments

{
  "GeneratedApis": {
    "RoutePrefix": "api",
    "SegmentsToSkipForRoute": 2,
    "IncludeCommandNameInRoute": true,
    "IncludeQueryNameInRoute": true
  }
}

Generated route: /api/Sales/Commands/CreateOrderCommand

Exclude Type Names

{
  "GeneratedApis": {
    "RoutePrefix": "api",
    "SegmentsToSkipForRoute": 3,
    "IncludeCommandNameInRoute": false,
    "IncludeQueryNameInRoute": false
  }
}

Generated route: /api/Commands (for commands) or /api/Queries (for queries)

Note: When IncludeCommandNameInRoute or IncludeQueryNameInRoute is set to false, the system automatically detects route conflicts. If multiple commands or queries exist in the same namespace (after skipping segments), the type name will be automatically included in the route to prevent conflicts. This ensures that:

• Single command/query in a namespace: Route remains clean without the type name
• Multiple commands/queries in the same namespace: Type names are automatically added to prevent route collisions
• Both runtime endpoint mapping and proxy generation apply this logic consistently

For example, with the configuration above:

• If you have only MyApp.Sales.Commands.CreateOrder, the route will be /api/commands
• If you have both MyApp.Sales.Commands.CreateOrder and MyApp.Sales.Commands.UpdateOrder, the routes will be /api/commands/create-order and /api/commands/update-order respectively (type names added automatically to avoid conflict)

Note

The runtime GeneratedApis settings and the build-time proxy-generation settings must agree. If you change route generation here, mirror it in the CratisProxies* MSBuild properties so the generated TypeScript clients call the same routes. See Proxy Generation Configuration.

JSON Serialization

Arc provides a centralized JsonSerializerOptions configuration through ArcOptions. This ensures consistent JSON serialization across your entire application, including controller actions, manual serialization, and generated API endpoints.

Default Configuration

Arc configures JsonSerializerOptions with the following defaults:

• Property Naming: Camel case with acronym-friendly handling (e.g., XMLParser becomes xmlParser)
• Null Handling: Null values are ignored when writing JSON
• Enums: Serialized as integers (not strings)
• Concepts: Full support for Cratis Concepts (strongly-typed primitives)
• Date/Time: Support for DateOnly and TimeOnly types
• Types: Support for System.Type and System.Uri serialization
• Derived Types: Polymorphic serialization support when derived types are discovered

Accessing JsonSerializerOptions

The configured JsonSerializerOptions is available through dependency injection:

public class MyService
{
    public MyService(JsonSerializerOptions jsonOptions)
    {
        // Use the Arc-configured options
        var json = JsonSerializer.Serialize(myObject, jsonOptions);
    }
}

Or through ArcOptions:

public class MyService
{
    public MyService(IOptions<ArcOptions> arcOptions)
    {
        var jsonOptions = arcOptions.Value.JsonSerializerOptions;
    }
}

Customizing JSON Serialization

You can add custom converters or modify the configuration through the options pattern:

builder.AddCratisArc(options =>
{
    // Add a custom converter
    options.JsonSerializerOptions.Converters.Add(new MyCustomConverter());
});

Any customizations made to ArcOptions.JsonSerializerOptions will automatically be applied to ASP.NET Core controller actions as well, ensuring consistency throughout your application.

Best Practices

1. Use Configuration Files: For most scenarios, use appsettings.json configuration as it allows easy environment-specific overrides without code changes.

2. Environment-Specific Settings: Leverage appsettings.{Environment}.json files for environment-specific configurations.

3. Programmatic Configuration: Use programmatic configuration when you need to:

   • Set configuration based on runtime conditions
   • Use custom identity providers
   • Override specific settings that can’t be easily expressed in JSON

4. Route Planning: Consider your API route structure carefully when configuring GeneratedApis options, especially in public-facing APIs where route stability is important.

5. Header Standardization: Use standard HTTP header names for correlation IDs and tenant IDs that align with your organization’s conventions and any API gateways or load balancers in use.

6. JSON Consistency: Always use the injected JsonSerializerOptions when manually serializing/deserializing JSON to maintain consistency with controller actions and generated APIs.