Bring a large pot of salted water to a boil. Cook the pasta according to package instructions, but add an extra 2 minutes to make sure it soft but still firm. Once cooked, drain and transfer to a large bowl.
Once the macaroni pasta has cooled, add the carrots, onions, pineapple (no need to drain), celery, roasted red peppers, and eggs.
In a small bowl, combine the mayonnaise, Dijon mustard, sugar, a generous pinch of salt, some ground pepper, and about 2 tablespoons of the reserved pineapple juice. Mix well until smooth and creamy.
Pour the dressing over the pasta and other ingredients. Gently mix everything together, until evenly coated with the dressing.
Taste and adjust the seasoning with additional salt, pepper, or sugar as needed. If the salad is dry, you can add a bit more pineapple juice.
Cover and refrigerate for at least 1 hour before serving to allow the flavors to meld together.
After refrigerating, you might find that it needs a bit more mayonnaise or pineapple juice. Adjust accordingly to maintain the desired creaminess.