Metaphor is a deep thing, it's very hard to discern the presence of which.
When I very learned the term. All I was is "no 'like or as'". Typically you say "is" to connect one thing to the other (which if I remember correctly are called "tenor" and "vehicle"), but a metaphor isn't really limited to it.
Now here are some examples, I am uncertain whether which are metaphors.
Book makes a great gift. (Whether books are great gifts)
The dance revolution was fought on many fronts, but the key battle took place at Vermont's Bennington College. ( dance revolution is a war? Anything else?)