Adding pergola to existing deck
I have a 12' x 16' deck. Construction is 2x10 ledger attached to house and two 2x10 beams sandwiched around three 6x6 posts (posts are set in concrete piers 4' deep). The beams are set in (cantilevered) about 15" from the outside edge of the deck. The joists are 16" on center and are 2x8's. Standard 5/4" decking for the surface.
I'd like to add a pergola to cover the deck and have some design questions about how to intergrate it safely.
Where can I attach the outer posts (those away from the house) to support the pergola? Do they have to be on top of the beams of the deck (which would set them about 15" into the deck surface)? Or, could I attach them to the outside of the 2x8 fascia board with lag bolts? Or, could I set them on the deck surface centered on a joist?
I'm not sure what a pergola would weigh and how that load would be spread on the deck. I figure I could use a ledger on the house to support one side of the pergola and 3 or 4 posts on the outside of the pergola which is the basis for the questions above.
Thanks for any advice.