You get multiple ones and failover to them or you schedule a maintenance window. Yes, it'll be more expensive, but you probably already have a good reason & the

You get multiple ones and failover to them or you schedule a maintenance window. Yes, it'll be more expensive, but you probably already have a good reason & the associated budget if you colocate as opposed to renting from Hetzner/OVH/etc. Is this so different from the cloud? Even an EC2 instance should be assumed to be a single point of failure and you also need multiple (preferably in different AZs or regions) if uptime is important.