Fill a large pot with water, then add the crab boil seasoning (depending on the size of pot, you may need to adjust the seasoning to your taste) and lemons and bring to a boil (this can be done on a grill or indoors). Add the potatoes, kielbasa and onions and cook until the potatoes are tender, about 15 minutes. Add the corn and cook an additional 5 minutes. Add the shrimp and cook until just cooked through, 2 to 3 minutes.
Drain and serve immediately with the melted butter and cornbread.