In addition to metal baluster systems that are used in combination with wood there are also rail systems composed completely of metal.  These rails are usually built from either powder coated aluminum or steel. 

Aluminum can be cut with a standard saw blade just like wood to be custom fitted to your design.  Steel will be more difficult to cut and may come in premanufactured panels for installation.  There also may be some welding involved. 

Metal rail systems are usually attached to the deck surface by bolting the rail posts into the framing.  In order to accomplish a solid connection you will be required to install blocking into the framing to provide a stable foundation for the posts.