Since you are looking for the industrial modern look, I would actually recommend leaving the rust. I think it looks great!

Rusting of stainless steel isn't uncommon, especially in high traffic areas where the metal is touched and in direct contact with other abrasives. Some abrasion is required to clean the steel since the rust needs to be physically (as opposed to chemically) removed. You can try the following on a small area and see how it works.

1. Mix 1 tbs of baking soda in 2 cups of water
2. Rub the solution on the rust area using a soft toothbrush.
3. Rinse the area and wipe with a damp paper towel. If it's working you should see the rust on the paper.

Once you have the railing clean you should apply Magic Stainless Steel Cleaner or a similar product to fight further rust formation. The stainless steel cleaner might even remove some areas of light rust.