.NET Aspire orchestration overview

Article
04/23/2024

.NET Aspire provides APIs for expressing resources and dependencies within your distributed application. In addition to these APIs, there's tooling that enables some compelling scenarios.

Before continuing, consider some common terminology used in .NET Aspire:

App model: A collection of resources that make up your distributed application (DistributedApplication). For a more formal definition, see Define the app model.
App host/Orchestrator project: The .NET project that orchestrates the app model, named with the *.AppHost suffix (by convention).
Resource: A resource represents a part of an application whether it be a .NET project, container, or executable, or some other resource like a database, cache, or cloud service (such as a storage service).
Reference: A reference defines a connection between resources, expressed as a dependency. For more information, see Reference resources.

Note

.NET Aspire's orchestration is designed to enhance your local development experience by simplifying the management of your cloud-native app's configuration and interconnections. While it's an invaluable tool for development, it's not intended to replace production environment systems like Kubernetes, which are specifically designed to excel in that context.

Define the app model

.NET Aspire empowers you to seamlessly build, provision, deploy, configure, test, run, and observe your cloud application. This is achieved through the utilization of an app model that outlines the resources in your app and their relationships. These resources encompass projects, executables, containers, as well as external services and cloud resources that your app depends on. Within every .NET Aspire app, there is a designated App host project, where the app model is precisely defined using methods available on the IDistributedApplicationBuilder. This builder is obtained by invoking DistributedApplication.CreateBuilder.

App host project

The app host project handles running all of the projects that are part of the .NET Aspire application. In other words, it's responsible for orchestrating all apps within the app model. The following code describes an application with two projects and a Redis cache:

var builder = DistributedApplication.CreateBuilder(args);

var cache = builder.AddRedis("cache");

var apiservice = builder.AddProject<Projects.AspireApp_ApiService>("apiservice");

builder.AddProject<Projects.AspireApp_Web>("webfrontend")
       .WithReference(cache)
       .WithReference(apiservice);

builder.Build().Run();

To help visualize the relationship between the app host project and the resources it describes, consider the following diagram:

Each resource must be uniquely named. This diagram shows each resource and the relationships between them. The container resource is named "cache" and the project resources are named "apiservice" and "webfrontend". The web frontend project references the cache and API service projects. By expressing a reference in this way, the web frontend project is saying that it depends on these two resources.

Built-in resource types

.NET Aspire apps are made up of a set of resources. There are three base types of compute resources:

Method	Resource type	Description
AddProject	ProjectResource	A .NET project, for example ASP.NET Core web apps.
AddContainer	ContainerResource	A container image, such as a Docker image.
AddExecutable	ExecutableResource	An executable file.

Project resources are .NET projects that are part of the app model. When you add a project reference to the app host project, the app host generates a type in the Projects namespace for each referenced project.

To add a project to the app model, use the AddProject method:

// Adds the project "apiservice" of type "Projects.AspireApp_ApiService".
var apiservice = builder.AddProject<Projects.AspireApp_ApiService>("apiservice");

Reference resources

A reference represents a dependency between resources. Consider the following:

var cache = builder.AddRedis("cache");

builder.AddProject<Projects.AspireApp_Web>("webfrontend")
       .WithReference(cache);

The "webfrontend" project resource uses WithReference to add a dependency on the "cache" container resource. These dependencies can represent connection strings or service discovery information. In the preceding example, an environment variable is injected into the "webfronend" resource with the name ConnectionStrings__cache. This environment variable contains a connection string that the webfrontend can use to connect to redis via the .NET Aspire Redis component, for example, ConnectionStrings__cache="localhost:62354".

Connection string and endpoint references

It's also possible to have dependencies between project resources. Consider the following example code:

var cache = builder.AddRedis("cache");

var apiservice = builder.AddProject<Projects.AspireApp_ApiService>("apiservice");

builder.AddProject<Projects.AspireApp_Web>("webfrontend")
       .WithReference(cache)
       .WithReference(apiservice);

Project-to-project references are handled differently than resources that have well defined connection strings. Instead of connection string being injected into the "webfrontend" resource, environment variables to support service discovery are injected.

Method	Environment variable
`WithReference(cache)`	`ConnectionStrings__cache="localhost:62354"`
`WithReference(apiservice)`	`services__apiservice__http__0="http://localhost:5455"` `services__apiservice__https__0="https://localhost:7356"`

Adding a reference to the "apiservice" project results in service discovery environment variables being added to the front-end. This is because typically, project to project communication occurs over HTTP/gRPC. For more information, see .NET Aspire service discovery.

It's possible to get specific endpoints from a container or executable using the WithEndpoint and calling the GetEndpoint:

var customContainer = builder.AddContainer("myapp", "mycustomcontainer")
                             .WithHttpEndpoint(port: 9043, name: "endpoint");

var endpoint = customContainer.GetEndpoint("endpoint");

var apiservice = builder.AddProject<Projects.AspireApp_ApiService>("apiservice")
                        .WithReference(endpoint);

Method	Environment variable
`WithReference(endpoint)`	`services__myapp__endpoint__0=https://localhost:9043`

The port parameter is the port that the container is listening on. For more information on container ports, see Container ports. For more information on service discovery, see .NET Aspire service discovery.

Service endpoint environment variable format

In the preceding section, the WithReference method is used to express dependencies between resources. When service endpoints result in environment variables being injected into the dependent resource, the format may not be obvious. This section provides details on this format.

When one resource depends on another resource, the app host injects environment variables into the dependent resource. These environment variables configure the dependent resource to connect to the resource it depends on. The format of the environment variables is specific to .NET Aspire and expresses service endpoints in a way that is compatible with Service Discovery.

Service endpoint environment variables start with services and are delimited by a double underscore __. They're prefixed with services__, followed by the service name, the service endpoint name or protocol, and the index. The index supports multiple endpoints for a single service, starting with 0 for the first endpoint and incrementing for each additional endpoint.

Consider the following environment variable examples:

services__apiservice__http__0

The preceding environment variable expresses the first HTTP endpoint for the apiservice service. The value of the environment variable is the URL of the service endpoint. A named endpoint might be expressed as follows:

services__apiservice__myendpoint__0

In the preceding example, the apiservice service has a named endpoint called myendpoint. The value of the environment variable is the URL of the service endpoint.

APIs for adding and expressing resources

Beyond the base resource types, ProjectResource, ContainerResource, and ExecutableResource, .NET Aspire provides extension methods to add common resources to your app model. The following table lists the methods and their corresponding resource types:

Cloud-agnostic resources are available in the following NuGet packages:

Method	Resource type	Description
`AddMongoDB(...)`	`MongoDBServerResource`	Adds a MongoDB server resource.
`AddMySql(...)`	`MySqlServerResource`	Adds a MySql server resource.
`AddNodeApp(...)`	`NodeAppResource`	Adds a Node.js app resource.
`AddNpmApp(...)`	`NodeAppResource`	Adds a Node.js app resource that wraps an NPM package.
`AddPostgres(...).`AddDatabase	PostgresDatabaseResource	Adds a Postgres database resource.
`AddSqlServer(...).`AddDatabase	SqlServerDatabaseResource	Adds a SQL Server database resource.
AddPostgres	PostgresServerResource	Adds a Postgres server resource.
AddRabbitMQ	RabbitMQServerResource	Adds a RabbitMQ server resource.
AddRedis	RedisResource	Adds a Redis container resource.
AddSqlServer	SqlServerServerResource	Adds a SQL Server server resource.

Azure specific resources are available in the following NuGet packages:

Method	Resource type	Description
AddAzureStorage	AzureStorageResource	Adds an Azure Storage resource.
`AddAzureStorage(...).`AddBlobs	AzureBlobStorageResource	Adds an Azure Blob Storage resource.
`AddAzureStorage(...).`AddQueues	AzureQueueStorageResource	Adds an Azure Queue Storage resource.
`AddAzureStorage(...).`AddTables	AzureTableStorageResource	Adds an Azure Table Storage resource.
AddAzureCosmosDB	AzureCosmosDBResource	Adds an Azure Cosmos DB resource.
AddAzureKeyVault	AzureKeyVaultResource	Adds an Azure Key Vault resource.
`AddRedis(...)`.AsAzureRedis	AzureRedisResource	Configures resource to use Azure for local development and when doing a deployment via the Azure Developer CLI.
`AddSqlServer(...)`.AsAzureSqlDatabase	AzureSqlServerResource	Configures SQL Server resource to be deployed as Azure SQL Database (server).
AddAzureServiceBus	AzureServiceBusResource	Adds an Azure Service Bus resource.

Important

The .NET Aspire Azure hosting libraries rely on Azure.Provisioning.* libraries to provision Azure resources. For more information, Azure provisioning libraries.

AWS specific resources are available in the following NuGet package:

📦 Aspire.Hosting.AWS

For more information, see GitHub: Aspire.Hosting.AWS library.