Vertical Slice coupling with Notifications – where should side-effects live?

[mikek9084]

Title: Vertical Slice Architecture – handling side-effects without cross-slice coupling

Hi 👋

I’m applying a vertical slice architecture with MediatR, and I’m running into a design concern around side-effects and coupling between slices.

Context

After each student is created, I want to fire:

StudentCreatedNotification

This notification is handled by multiple handlers:

• StudentReminderWorker
• StudentViewedNotificationHandler

Current command handler:

public class CommandHandler : IRequestHandler<Command, int>
{
    private readonly SchoolContext _db;

    public CommandHandler(SchoolContext db) => _db = db;

    public async Task<int> Handle(Command message, CancellationToken token)
    {
        var student = new Student
        {
            FirstMidName = message.FirstMidName,
            LastName = message.LastName,
            EnrollmentDate = message.EnrollmentDate!.Value
        };

        await _db.Students.AddAsync(student, token);
        await _db.SaveChangesAsync(token);

        mediator.get().publish(
            StudentCreatedNotification(student.Id)
        );

        return student.Id;
    }
}

Problem

Now the Student vertical slice is directly aware of and publishing a notification that belongs to another module/slice.

This introduces coupling between:

• Student slice (core business behavior)
• Notification/Worker slices (side-effects)

Which feels like it breaks vertical slice isolation.

Questions

1. Where should this kind of side-effect live in a vertical slice architecture?
2. How do you avoid coupling between slices when publishing notifications/events?

Would really appreciate guidance