Remove excess fat from chicken pieces. Rub on garlic powder and cayenne. Let stand 30 minutes. In a bowl combine onions, pepper and celery. Set aside. Combine flour, 1/2 teaspoon salt, 1/2 teaspoon garlic powder and 1/2 teaspoon cayenne in a plastic bag. Add chicken pieces and shake. Reserve 1/2 cup flour.
In a heavy skillet heat 1 inch oil to very hot. Fry chicken until brown (5-8 minute side). Drain on paper towels. Pour cooled oil into glass measuring cup. Scrape pan bottom and return 1/2 cup oil to the pan. Place pan over heat; whisk in remaining 1/2 cup flour. Cook; whisk constantly until roux is red brown (3-4 minutes). Don't scorch. Remove from heat and add vegetables. Cook until vegetables are soft. Scrape pan bottom.
Place stock in large Dutch oven. Bring to boil. Add roux mixture tablespoons at a time. Reduce heat to simmer; stir in Andoville sausage and minced garlic. Simmer 45 minutes. Bone cooked chicken; cut meat into 1/2 inch chunks. Stir in chicken. As a main course, serve 1/3 cup rice in soup bowl with 1 1/4 cups gumbo.
