reqwest::blocking::Client::new builds a shell tokio runtime to check it is safe to block, then drops it; in a debug build only, dropping that runtime panics when the calling thread already belongs to one that forbids blocking, which is exactly what an async task on the server's own runtime is. spawn_blocking runs on a thread the runtime marks safe to block, so the same construction there does not panic. A new test in route53.rs proves both halves, so a reqwest upgrade that changes this behavior does not go unnoticed. Change-Id: Icc65197b47856946da80d4f8af86d0792097a5fb