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Distributed Systems with .NET

9: Autobarn Exercises

Exercise: Autobarn.MailSender

Create an additional service as part of the Autobarn stack, that will send an email every time we get the price for a new vehicle.

The service should:

  • Subscribe to NewVehiclePriceMessage messages
  • Use the Microsoft.Extensions.Hosting package and run as a hosted service

Use an online service such as Mailtrap to get a test SMTP connection you can use to send (and view) email messages.

Exercise: Vehicle Condition

We’ve been asked to include the condition of the vehicle in the Autobarn listing process.

Vehicles can be:

  • New
  • Used (Good)
  • Used (Fair)
  • Used (Poor)
  • Non-runner
  • Write-off

The vehicle condition needs to be reflected at every stage of the process:

  • The HTTP API exposed on the Autobarn website should require the vehicle condition to be specified when listing a new vehicle for sale
    • Question: how should the client specify the condition?
    • Question: does the API need to expose a list of vehicle conditions somewhere?
  • The NewVehicleMessage publishers and subscribers will need to capture and preserve this new field when publishing messages about new vehicles
  • The PricingServer should take the vehicle condition into account when calculating prices
    • Exactly how we do this is up to you :)
  • The website notifications should include the condition of the vehicle in the pop-up that’s displayed to website visitors

Exercise: Vehicle Status

There’s an online service that will let us check the reported status of a vehicle:

https://ursatile-vehicle-info-checker.azurewebsites.net/api/CheckVehicleStatus?registration={reg}

This service will return a plain text string response:

  • OK - The vehicle is OK
  • STOLEN - the vehicle has been reported stolen
  • WRITTEN_OFF - the vehicle has been registered as written off
  • INVALID - you have not specified a valid vehicle registration

Add a new microservice called Autobarn.StatusChecker to the Autobarn application which will query a vehicle status BEFORE calculating the vehicle price.

  • If the vehicle is reported stolen, the status checker service should use the HTTP API and send a DELETE request to remove the vehicle from the database
  • If the vehicle is written off, ensure the status in the NewVehicleMessage reflects this.
  • Your service should publish a VehicleStatusValidated message
  • You’ll need to update the Autobarn.PricingClient to subscribe to VehicleStatusValidated, so that we only calculate a price AFTER we’ve confirmed the vehicle status.