cvoytek,
I'm not sure what you mean by " aren't you risking bending the rail?"
I'm planning on building my deck next to the pool like Huskerfan's pictures show, leaving 1/2" - 1" gap between the two structures, the only way I can see bending the rail would be if people walk on it, however, in my case, teh pool structure is blow molded resin, it's extrmely strong, and the likely hood of anyone walking on it is slim to none.
My deck will be built on a floating foundation - I think it will heave/settle with frost about the same as the pool.
However, if you use sonotube and go over your rail, you are limiting how much frost expansion can occur, once you hit your maximum, the pool will push up into the underside of the deck and the wall will crush, if you go under the rail and the pool settles beyound where it is now, the pool rail will end up sitting on your deck and may separate from the remaining structure if the pool settles even more. Leaving a small gap between the two should allow for them to act as sepaprate entities without any interference to each other.