Attach railing to aluminum post
If you can find these self tapping metal bits, they will do the trick. 

They are a lot more robust then they look. I couldn't find the gauge of the post but worse case scenario you could mount a block to the post using two self trappers and go through the railing mount with a third self trapper. 

simply google

from a google search

The list of nobility is quite complicated, it's not meant for the typical tradespersons to understand. A galvanic reaction is used to galvanize a material to prevent it from having a reaction as a result of a large gap in nobility. Materials are galvanized to reduce galvanic reaction. Now get off my back. 

also from a google search