Handrails come in the following types:
Wood (common in new construction but does not last)
Plain welded steel call wrought iron – (does not last and rusts need maintenance)
Vinyl – Lifetime warranty (various picket sizes and styles exist but the posts will be 4x4?)
Aluminum - Lifetime warranty (centered line posts are normally 2x2” but corner and end posts are typically 3”x3” and protrude above the top rail)
Cable – Stainless steel with extended warranty
Glass with no posts or aluminum posts and top rail (centered line posts are normally 2x2” but corner and end posts are typically larger and protrude above the top rail)
Either they support a water proof decking surface or one where the water goes between the decking boards.
If the deck is not water proof the posts can be mounted either on top of the deck or on the side just off of the deck.
If the deck is water proof it is not recommend that they be mounted on top of the deck surface but only off to the side to keep the attachment bolts from penetrating the decking membrane or surface.
New Construction considerations:
Before a deck is framed up the type of handrail to be used and how it is to be attached needs to be decided. If for instance a bolt down from the top approach is to be used enough decking substructure needs to be placed under each post to the attachment is solid. If a side mount then the fascia wood needed should be defined.
If outside posts are to be attached to the rim joist around the perimeter of the deck, then most likely double posts will be needed for each outside corner. A few of the metal rail systems make a special bracket that will support a post that protrudes from the corner that can connect to runs in two different directions.