Ruddock, who only turned 19 last month, and Ryan played for the Ireland Under-20s last season and took part in the recent training camp for Allen Clarke's U-20 squad.
With Devin Toner locking down alongside Malcolm O'Kelly, the Leinster team will be led by hooker Bernard Jackman this weekend.
Behind the scrum, Ireland 'A' centre Fergus McFadden will partner Eoin O'Malley in midfield. O'Malley, the third debutant in an exciting Leinster line-up, is 21 and hoping to make his mark at senior level after a promising underage career.
Chris Keane, the elder statesman of the back-line at 31, will partner another talented youngster Ian McKinley at half-back, with David Kearney and Simon Keogh starting on the wings.
Speaking ahead of Sunday's game, the 20-year-old Kearney said that the squad are keen to maintain pole position in the league against a vastly improved Dragons side.
"This will be the third time that I will come up against the Dragons in the last six months and they are a side who impress me because they play a fast, attacking game with pace out wide and they will be a handful at Rodney Parade," said Kearney, a younger brother of Ireland and Lions star Rob.
"It will be a good test for us coming off the back of two good wins in the British & Irish Cup and we're all conscious that we need to maintain our position in the league.
"It (Rodney Parade) is a tough place to go. A number of players, including myself, made our senior debuts there in the closing game of last season and we didn't exactly cover ourselves in glory. We're conscious of that.
"Opportunities like this don't always come about in mid-season to make an impression on the coaching staff, so we're all excited about Sunday's match."
He added: "I have been pleased enough with my own form in the British & Irish Cup. In both wins, the wingers were fairly starved of the ball out wide but hopefully Sunday will provide more chances to get my hands on the ball.
"Training has been sharp with the Ireland 'A' players returning to training after being away for the last few weeks. The standard of training goes up another notch and it's great to train with the senior internationals.
"You have to feed of that experience and it gives you a good buzz and re-focuses the mind for the task at hand.
"Everyone's fresh, focused and determined to keep our place at the top of the league."
LEINSTER (v Newport Gwent Dragons): Niall Morris; David Kearney, Eoin O'Malley, Fergus McFadden, Simon Keogh; Ian McKinley, Chris Keane; Ronan McCormack, Bernard Jackman (capt), CJ van der Linde, Devin Toner, Malcolm O'Kelly, Rhys Ruddock, Dominic Ryan, Stephen Keogh.
Replacements: Richardt Strauss, Mike Ross, Trevor Hogan, Paul Ryan, Paul O'Donohoe, Ian Madigan, Michael Keating.