When we moved to Moraga, the railing around the back deck was a bit shaky.
"A bit" is understatemtnt. You could push and pull it back and forth, several inches.
That railing is now rock solid. There are triangles supporting the posts, under the deck.
Posts are spaced so that there is a cut out in each one, that rests on a deck joist.
Then the post continues down another 15", and there's a brace that connects the bottom to the joist.
Those posts, DO NOT MOVE. There are 3 pics of the part of the post under the deck.
I showed it to a contractor one time and he said, "I'm going to do that next time."
There are 7 posts along the 50' of deck about, but not exactly, 8' apart, on the upper level of the back of the house. It's between 20' and 30' to the ground below. (I did tell you the house was on a hill.) There are 3/8" stainless steel bolts that attach each post to: The joist that it rests on, The brace at the bottom, And a 3rd that attaches the other end of that brace, to the joist, 4-5' in from the end. The posts and joists are all redwood, that is not as strong as pressure treated fir, but will last just as long, and won't damage any hardware they come in contact with. Pressure treated wood is very good, but the acid in it would rot a nail away to almost nothing in a couple years. (Yeah, the ground is way down there.) The braces are quite long, and reach nearly to the deck supports of the cantilevered deck.