Sometimes i had a 5-10% ping loss between servers in the same Hetzner datacenter, so not being on the same rack can be a problem. Especially if you are using nginx -> backend. Then every request is a TCP connect to the backend server, and when SYN packet is lost, you will have a 3 seconds timeout (at least on FreeBSD TCP stack).
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Sometimes i had a 5-10% ping loss between servers in the same Hetzner datacenter, so not being on the same rack can be a problem. Especially if you are using nginx -> backend. Then every request is a TCP connect to the backend server, and when SYN packet is lost, you will have a 3 seconds timeout (at least on FreeBSD TCP stack).