IMO, "make your servers fungible" is a better way to express the intent: slightly shorter, no metaphors, although "fungible" is a less common word. Maybe that's just me. (Edited to add: "make your tests fungible" has I think the wrong connotation; I think the original wording on the blog is about test executions -- and "make your test executions fungible" does seem like a good goal, similar to ACID guarantees for database transactions.)
Before that, I used to call them "ephemeral", and of course half the people asked what "ephemeral" means, probably "fungible" would be met with similar question, unless the crowd is cryptocurrency-adjacent, that term seems understood there.