Hello,
As such there is no interaction between the two i.e. Keflex( cephalexin) and alcohol, but it is best to avoid alcohol when you are taking any drug. For more information it will be best that your friend discusses this with his doctor.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.