I feel like even Amazon/AWS wouldn't be that dim, they surely have professionals who know how to build somewhat resilient distributed systems when DNS is involved :)
I doubt a circular dependency is the cause here (probably something even more basic). That being said, I could absolutely see how a circular dependency could accidentally creep in, especially as systems evolve over time.
Systems often start with minimal dependencies, and then over time you add a dependency on X for a limited use case as a convenience. Then over time, since it's already being used it gets added to other use cases until you eventually find out that it's a critical dependency.
