Solution attempt for the Web Monitoring domain modeling.

WebAppAggregate.cs

/* File structure:
 * /Domain/WebMonitoring/WebAppAggregate/WebApp.cs
 * /Domain/WebMonitoring/WebAppAggregate/WebAppService.cs
 * /Domain/WebMonitoring/WebAppAggregate/IWebAppRepository.cs
 * /Domain/WebMonitoring/WebAppAggregate/IHttpStatusChecker.cs
 *
 * This way, the Aggregate itself is not "materialized" as a class or any programming resource.
 * It is a concept, and its invariants are enforced by the WebApp (entity, aggregate root) and
 * WebAppService.
 */

public class WebApp : Entity, IAggregateRoot
{
	public Guid Id { get; private set; }
	public string Name { get; private set; }
	public Url Url { get; private set; }
	public bool IsAlive { get; private set; }
	
	public WebApp(Guid id, string name, Url url)
	{
		// Validation goes here...
		// If ok, set properties. Throw exception, otherwise.
		
		this.AddDomainEvent(new WebAppRegisteredEvent(id, name, url));
	
		Id = id;
		name = name;
		Url = url;
	}
	
	public void UpdateIsAlive(bool isAlive)
	{
		if (isAlive != this.IsAlive)
			this.AddDomainEvent(new WebAppStatusChangedEvent(Id, oldStatus: IsAlive, newStatus: isAlive));
	
		IsAlive = isAlive;
	}
}

public class WebAppService
{
	private readonly IWebAppRepository _repository;
	private readonly IUnitOfWork _uow;
	private readonly IHttpStatusChecker _httpStatusChecker;
	
	public WebAppService(IWebAppRepository repository, IUnitOfWork uow, IHttpStatusChecker httpStatusChecker)
	{
		_repository = repository;
		_httpStatusChecker = httpStatusChecker;
	}
	
	public Result RegisterWebApp(Guid id, string name, Url url)
	{
		var webApp = new WebApp(id, name, Url);

		var addResult = _repository.Add(webApp);
		if (!addResult.OK) return Result.Fail(addResult.Errors);
		
		var commitResult = _uow.Commit();
		if (!commitResult.OK) return Result.Fail(commitResult.Errors);
		
		return Result.OK;
	}
	
	public Result UpdateWebAppStatus(Guid id)
	{
		var webApp = _repository.GetById(id);
		if (webApp == null) return Result.Fail($"Web App '{id}' not found");
		
		var status = _httpStatusChecker.GetStatus(webApp.Url);
		var isAlive = (status == 200);
		
		webApp.UpdateIsAlive(isAlive);
		
		var updateResult  = _repostory.Update(webApp);
		if (!updateResult.OK) return Result.Fail(updateResult.Errors);
		
		var commitResult = _uow.Commit();
		if (!commitResult.OK) return Result.Fail(commitResult.Errors);
		
		return Result.OK;
	}
}