I'm getting an error "This site can’t be reached"
In a clustered install, if you're intermittently receiving an error "This site can’t be reached. Domain.com took too long to respond." but all nodes/DNS/etc appear to be configured correctly, it's possible that your load balancer layer has run out of disk space.
Running out of disk space in a load-balanced environment prevents the balancer from properly persisting your session to disk and will result in no data being returned from the environment.