My coconut also had pests eariler this year, but it wasnt aphids, but scale. I poured some dishsoap mixed with water and applied to every leaf down to the stem and trunk. Then I washed it all off. A few days later I got a paper towel and poured rubbing alcohol on it and rubbed every single one off the plant. It took a few weeks before I got them all, but I havent seen them back since. This happened in the fall to me so I had to do all this indoors. Outside you have access to fresh air and a powerful hose so you can also soak it with water often which could wash some lose ones away.
Other than some leaf discoloring, the scale didnt seem to do too much permanent damage to my coconut and its now growing well so it seems like as long as you get rid of the aphids quick, you coco will not be affected as much.

Good luck!

Water & soap work well for Aphids and Coffee grounds works well for Scale. Good luck!

Neem oil,or as Jay said Coffee,probably fastest to make some up and spray it on too.

I hear neem oil works great. Im a little afraid to try coffee grinds because everything I put it in seems to die, but maybe its not pure coffee or something. Just make sure your not putting something like hazelnut coffee in there, I dont think it will be too happy with anything but pure coffee but I could be wrong.

Good luck!

I put about 2 lbs of mixed coffee from Starbucks around and all over my palms and they love it. It cured the Scale infestation that I had from last fall. It honestly won't hurt anything, but I do understand the concern. I was leery at first too, but it does work and also, from what I hear, it works as a fertilizer as well. I add coffee grounds about once per month now.

I'm attaching a link, the one that I found when searching for a Scale cure. Give it a read if you get a chance... it's very informative.

Here is a link that might be useful: Coffee grounds

Thanks for the info jay. It seems like most people are finding coffee to be very helpful. I dont think I would try it again unless I have a plant that is very infested with scale and if it works then I will probably be less afraid to use it. Fortunately most of my plants are finally bug free for now!

Good luck!

Thanks everyone:) Wow, it looks like this dish soap mix kills them quicker than I thought?!