Table of contents

1. The BarManager application
2. Basic version of Clean Architecture
3. MediatR
4. Azure Table Storage
5. Azure Service Bus

• Configure the publishing in the Bartender project
• Configure the subscription in the Waitress project

6. SignalR server setup
7. Azure Blob Storage
8. Dockerfile creation

The BarManager application

The Barterder project exposes an Api to get, create, rename, delete and order drinks. The storage that is used will be Azure Table Storage. Ordering drinks puts a message with contract OrderPlaced on the Azure Servicebus.

The Waitress.Api project listens to the same Azure ServiceBus topic for an OrderPlaced message, which puts a message on the SignalR 'TablesHub' for clients to subscribe on. It also creates a receipt file on the Azure Blob storage which contains the data of the order.

The Tables project is a demo client for the SignalR Hub created in SignalR server setup.

Basic version of Clean Architecture

Drinks feature

Domain

• Entities, currently only Drink
• Interfaces for the repositories for the entities
• DomainEvents when an entity is changes (not used in this sample app)

Application

• CQRS
  • Commands: do actions on the entities
  • Queries: query for entities and their data
  • Handlers: contains the handle methods for the commands and queries when they are sent to the Mediator
• Defines and uses the interfaces to cross cutting concerns like database, eventbus, ...

Infrastructure

• Implementations of the cross cutting concerns like which database, which type of eventbus, ...

Api

• Controllers
  • These will send the command/query request to the IMediator
• Dto's for the actions
  • FluentValidation on dto's (configured in Startup using

services.AddControllers()
  .AddFluentValidation(configuration => configuration.RegisterValidatorsFromAssemblyContaining<Startup>()))

MediatR

Install Nuget package MediatR.Extensions.Microsoft.DependencyInjection Uncomment

services.AddMediatR(typeof(Startup));

Make the Commands and queries implement IRequest<>

MediatR has no distinction between Commands and queries, everything is a Request. This distinction can be created with an interface for each:

public interface ICommand : IRequest<Unit> { }

public interface IQuery<out T> : IRequest<T> { }

And for the handlers:

public interface ICommandHandler<in TCommand>
    : IRequestHandler<TCommand> where TCommand : ICommand { }

public interface IQueryHandler<in TQuery, TResult>
    : IRequestHandler<TQuery, TResult> where TQuery : IQuery<TResult> { }

Events inherit from INotification<>

Implement the Command & Query Handlers

See branch 1_implement_mediator for both implemented handlers The OrderDrink command is currently not being handled, because this will use the EventBus in a later stage

Use the IMediator in the controllers

The IMediator will be used in the controller to dispatch the commands and queries to their registered handlers (which is done by convention through DI)

• Using the Send() method, a request/response pattern is used
  • This means that only one handler can handle the request and a response is expected (Unit, an empty response, is also a response)
• Using the Publish() method, a pub/sub or publish/subscribe pattern is used
  • This means that multiple Handlers can listen to this and no response is expected

Azure Table Storage

In Azure Portal:

1. Create resource group with name
2. Create Storage Account in the resource group
3. In the Storage Account, under Table service, create a new Table called Drinks

In the Bartender project, add the required NuGet package: Microsoft.Azure.Cosmos.Table Set the ConnectionString and TableName in the appsettings.json file

Set up Azure Table Storage in the domain

Important for DDD/Clean Architecture: Azure Table Storage is not the best way to store entities, because it requires a mutable entity (public parameterless ctor, public setters). This application is just a demo for the Azure services. You should keep the domain model agnostic of any implementation details like what storage is used.

Make the Drink entity implement TableEntity, add a public parameterless ctor and public setters to all properties Make the Id a get-only to the RowKey property, which Table Storage uses internally. Set the PartitionKey to the name of the Entity class. See the 2_table-storage branch for the inplementation of the new Drink class

Register the CloudTableClient in DI in the Startup class in ConfigureServices:

services.AddTransient(provider =>
{
    var options = provider.GetService<IOptions<TableStorageSettings>>();
    if (options == null)
    {
        throw new NullReferenceException("Table Storage Settings are not set in the configuration");
    }

    CloudStorageAccount cloudStorageAccount = CloudStorageAccount.Parse(options.Value.ConnectionString);
    return cloudStorageAccount.CreateCloudTableClient();
});

Implement the AzureTableStorageRepository using the CloudTableClient through DI See the 2_table-storage branch for the inplementation

Register the new AzureTableStorageRepository in DI as implementation of IDrinksRepository

// services.AddSingleton<IDrinksRepository, InMemoryDrinksRepository>();
services.AddTransient<IDrinksRepository, AzureTableStorageDrinksRepository>();

Azure Service Bus

In the Azure Portal:

1. Create a Service Bus (Integration > Service Bus) in the same resource group
   • Make sure to select Standard or Premium price tier for Topic support
2. Under Entities > Topics, create a Topic called drinkorders
3. On the Topic, create a Subscription called waitress with a max delivery count of 10

In the Bartender and waitress project, install the NuGet package Microsoft.Azure.ServiceBus Get the connection string from the Service Bus Namespace > Settings > Shared access policies > RootManagedSharedAccessKey Set the ConnectionString and TopicName in the appsettings.json file in the Bartender project Set the Connectionstring, TopicName and SubscriptionName in the file in the Waitress project

Configure the publishing in the Bartender project

Register a new TopicClient with the settings as an ITopicClient:

services.AddSingleton<ITopicClient>(serviceProvider =>
{
    ServiceBusSettings serviceBusSettings = serviceProvider.GetRequiredService<IOptions<ServiceBusSettings>>().Value;
    return new TopicClient(serviceBusSettings.ConnectionString, serviceBusSettings.TopicName, RetryPolicy.Default);
});

In the Infrastructure layer, add a concrete implementation of the IEventBus as AzureEventBus that uses the TopicClient to publish to the Topic with the message as a serialized JSON string See the implementation in the 3_service-bus branch

Register the new AzureEventBus as the IEventBus:

// services.AddTransient<IEventBus, NullEventBus>();
services.AddTransient<IEventBus, AzureEventBus>();

Use the IEventBus in the DrinksCommandHandler to publish an OrderPlaced message on the ServiceBus when an OrderDrinks command is sent through the Mediator.

The Bartender will now put a message on the ServiceBus when an order is placed.

Configure the subscription in the Waitress project

Add a BusListener BackgroundService, which will register to the Subscription on the ServiceBus to listen when a message arrives. When it arrives, publish an OrderPlacedMessageReceived event through the Mediator which is already configured on the Waitress project. This will trigger all subscribed handlers to do their action when it is published. In MediatR, the subscribed handlers implement INotificationHandler<TEventType>. See the Handlers folder in the 3_service-bus branch. For the background listener implementation, see the BusListener.cs class.

Register the BusListener as ASP.NET Core HostedService in the Startup.cs:

services.AddHostedService<BusListener>();

Now, when a message is received from the ServiceBus, the NotificationHandler's Handle method will be called.

SignalR server setup

The TablesNotificationHandler will be used to signal client connected to the Tables SignalR Hub that a new Order will be delivered. To set this up, add SignalR in the Waitress project's Startup.cs which is included in the Microsoft.AspNetCore.App shared framework.

services.AddSignalR();

To enable scaling horizontal of a SignalR Server (multiple instances/replicas), a backplane should be used to share the state between them. This can be an Azure SignalR service or a Redis database. To add the Azure SignalR service as a backplane, create the service in Azure and add AddAzureSignalR to the SignalR registration

services.AddSignalR().AddAzureSignalR(Configuration["SignalRConnectionString"])

For this demo, we will skip adding a backplane.

Create a TablesHub inheriting from the Hub base class

Register an endpoint "/tables" for the new Tables Hub in the Startup.cs:

endpoints.MapHub<TablesHub>("tables");

Setup the TablesNotificationHandler to send the OrderedDrinks from the notification to all clients listening to an invocation of the Deliver method on the TablesHub using the injectable IHubContext<TablesHub> (more info). The method does not have to exist on the TablesHub, because it will be sent directly to the clients.

See the 4_signalr-server branch for the implementation. Start the Tables project together with both Api projects to test this functionality.

Azure Blob Storage

Azure Blob storage is used as file storage for any type of file.

1. In the Azure Portal, go to the previously created Storage account
2. Under Blob service > Container, create a new Blob container called 'receipts' with private access level
3. Get the Storage account ConnectionString from Settings > Access keys

Put the ConnectionString appsettings.json of the Waitress project under Azure:BlobStorage. Set the ContainerName to 'receipts'

Add the NuGet packages to the Waitress project: Azure.Storage.Blobs (important, get v12.7.0, 12.8.0 has a bug) and Microsoft.Extensions.Azure

Register the BlobServiceClient in an AzureClients builder in the Startup.cs:

services.AddAzureClients(builder =>
{
    builder.AddBlobServiceClient(Configuration[$"{BlobStorageSettings.ConfigurationKey}:ConnectionString"]);
});

Use the BlobServiceClient and the ContainerName from the BlobStorageSettings to upload a receipt to the Blob Container in the ReceiptNotificationHandler. The Stream required to upload is found on the OrderPlacedMessageReceived as .AsCsvStringStreamForBlobStorage(). See implementation in 5_blob-storage

Dockerfile creation

Docker

Add Docker support to both the API projects, using Linux containers (these are cheaper as VMs on AKS later on)

This creates the Dockerfiles. Visual Studio will build the images as well if Docker Desktop is running.

• You can list the installed images by using docker images
• To run a container using the docker image, use docker run <image-name> (add -d to have the console back after starting the docker container)
• See the running containers using docker ps (add -a to also see stopped containers)
• Stop a container using docker stop
• See help of all commands using docker or adding --help after the command you need help for

If the application will be deployed to a webserver with a reverse proxy in front that will handle the HTTPS redirection, remove this from the Startup.cs (more info):

// app.UseHttpsRedirection();

Docker Compose

Docker compose can start multiple containers at once. Add support for Container orchestration on one of projects.

If the project has HTTPS support, you need to create a self-signed dev certificate that will be added to the container. Remove the existing dev certificates:

dotnet dev-certs https --check --verbose
dotnet dev-certs https --clean
dotnet dev-certs https --check --verbose

Create a new certificate using the command dotnet dev-certs https -ep $env:appdata/ASP.NET/Https/dev.pfx -p password Trust the new certificate on your system to have it used for all HTTPS projects in .NET Core and 5 dotnet dev-certs https --trust In the docker-compose.override.yml, add the configuration for the new certificate to the environment variables of the projects:

environment:
    - ASPNETCORE_HTTPS_PORT=5011
    - ASPNETCORE_Kestrel__Certificates__Default__Password=password
    - ASPNETCORE_Kestrel__Certificates__Default__Path=/root/.aspnet/https/dev.pfx

The volumes to the /root/.aspnet/https container path were added by Visual Studio

Add the ports mapping for the exposed ports for each project in the docker-compose.override.yml file:

ports:
    - 5000:80 # The container exposes port 80, map it to 5000
    - 5001:443 # The container exposes port 443, map it to 5001

• Start the docker compose using docker-compose up (add -d to have the console back after starting)
• Logging can be viewed using docker-compose logs (add -f for watch mode)
• Stop the containers using docker-compose down