Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x13 inch pan.
Sift flour, baking soda, and cinnamon together in a bowl; set aside.
Stir sugar and oil together in a large bowl, until combined. Beat in eggs, one at a time, then stir in vanilla. Stir in flour mixture just until incorporated. Fold in carrots, pineapple, walnuts, and coconut. Pour batter into prepared pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 45 minutes. While still warm, poke holes in cake with a fork.
For the glaze: Combine sugar, butter, buttermilk, and vanilla in a saucepan. Bring to a boil over medium heat, then reduce heat and cook 5 minutes. Pour glaze over warm cake, then allow to cool completely.
Grandma's Carrot Cake · Dinner Match Lab | Dinner Match Lab