Director of football Nick Hammond is sure the stopper will prove to be a valuable asset in a similar vein to Kevin Doyle and Shane Long who also signed from Cork in 2005.
"We are delighted to have secured Alan's signature," Hammond told the club's official website.
"The discussions with Cork City have been quite lengthy but always courteous and professional and we're happy that things have now been concluded.
"We became aware of Alan when we signed Kevin Doyle and Shane Long and have monitored his progress since then.
"It's a massive challenge for Alan, but we're confident he can replicate the success of the other two boys."