Parse nested map from a YAML document

I am having trouble with (what I believe to be) a simple issue.
I am trying to create a CLI using commando, and this CLI will read a configuration yaml, and then do stuff. However, I am stuck at the parsing of the config.yaml
The following is my code:

type Config struct {
	Apps map[string]App `yaml:"apps"`
	Branch string  `yaml:"branch"`
}
type App struct {
	hostName string `yaml:"hostName"`
}
.
. //func main, and other standard stuff goes here
.
commando.
		Register("read").
		AddArgument("config", "read yaml file", "./config.yaml").
		SetAction(
			func(args map[string]commando.ArgValue, flags map[string]commando.FlagValue) {
				    //args["config"] equates to ./config.yaml and I will give that below
				    file, err := ioutil.ReadFile(args["config"].Value)
					if err != nil {
						log.Fatal(err)
					}

					var data2 Config
					err3 := yaml.Unmarshal(file, &data2)
					if err3 != nil {
						log.Fatal(err3)
					}
					fmt.Printf("Ad demo?: %#v\n", data2.Apps["ad-demo"].hostName)
					fmt.Printf("Data 2: %#v\n", data2)
			})
		commando.Parse(nil)

My config.yaml is as follows:

apps:
  ad-tag:
    hostName: ad-tag1.krg.io
  ad-demo:
    hostName: demo1.krg.io
branch: KAT-3821

This works for the most part. The problem is that the following prints:

Ad demo?: ""
Data 2: main.Config{Apps:map[string]main.App{"ad-demo":main.App{hostName:""}, "ad-tag":main.App{hostName:""}}, Branch:"KAT-3821"}

The hostName is coming up as an empty string.

Any idea as to what I am doing wrong? I feel like this should be very simple, but I cannot for the life of me figure out what I am doing wrong.

Thanks

Hostname should be exported, i.e. capitalized

type App struct {
    HostName string `yaml:"hostName"`
}

If you don't export it, packages such as yaml or json won't be able to read the field and populate it.