Outdoor dog food storage containers need to be able to withstand the elements. Many people who keep their dogs outdoors like keeping their food close by their dogs. You want a container that will keep insects and small animals out. Metal and plastic are your best options for these types of containers.
You also have the option of having automatic feeders with some of these units. They are typically gravity fed dispensing of the dog food, but should be mounted to something sturdy as your dog will be nudging these units. While they are free standing, mounting them will keep them extremely sturdy and prevent them from being accidentally turned over.
There are other containers that some people call 'outdoor' but really don't stand up to their claim. Bergan Stack-n-Stor is one option that should NOT be considered for outdoor use, because it is not airtight - consider the Bergan Smart Storage system instead. And while IRIS are great containers in general, I don't know if they are really designed to handle the elements. Most people who use IRIS containers outdoors are keeping them in the garage or car port - in which case, they work beautifully for that.