When an ESXi host is unable to forward its logs to a remote syslog server, a VMkernel Observation (VOB) is automatically raised by the host and it can be used to proactively alert administrators, which has been possible since ESXi 5.0 .... per this blog post from 2012 after some Googling! 😅😂
While I was pretty confident the behavior described above still holds true for our latest ESXi 7.x and 8.x releases, I wanted to be sure before responding back to a colleague. I deployed the latest ESXi 7.0 Update 3q and ESXi 8.0 Update 3b and after configuring syslog forwarding, I disabled the NIC on my Aria Operations for Logs to simulate a network disconnect and I saw the following log entry in /var/log/vobd.log
2024-09-28T21:12:00.298Z: [UserLevelCorrelator] 7452916537us: [esx.problem.vmsyslogd.remote.failure] The host "192.168.30.62:514" has become unreachable. Remote logging to this host has stopped.
By default, ESXi will attempt to retry the remote syslog connection after the configured timeout (default 180 seconds), which is a relatively new configuration option that is available with ESXCLIÂ (esxcli system syslog config set --default-timeout XX).