def split_tag(image_name):
    """Split docker image by image name and tag"""
    image = image_name.split(":", maxsplit=1)
    if len(image) > 1:
        image_repo = image[0]
        image_tag = image[1]
    else:
        image_repo = image[0]
        image_tag = None
    return image_repo, image_tag