For several years vSphere admins have been able to use the Log Insight tool for free as a “25 OSI” license was included in vCenter. This has meant that deployments of up to 24 hosts (plus vCenter) have been able to use the VMware tool as a syslog server and troubleshooting tool without having to purchase further licenses.
Due to changes in licensing this is no longer possible- see KB55980: vRealize Log Insight for vCenter Server – End of Availability (EOA). Version 4.6.x of Log Insight was the last to support this free license. This KB was released summer 2018, but now (spring 2019) it’s becoming particularly relevant because of the release cycle of vCenter.
vCenter 6.7 Update 2 has recently been released, and using the VMware product compatibility matrix you can see that this requires existing Log Insight installations to be upgraded to 4.8 as Log Insight 4.6.x (and therefore the “free” license) is not compatible. So be aware, without proper preparation patching your vCenter can break your established log management environment.
To keep running Log Insight in this environment it will be necessary to now purchase separate licenses from VMware. Talk to your re-seller or VMware account manager about this as there are options for both replacing the OSI licensing model or switching to a per-CPU model which would also enable the product to collect logs from any number of guest VMs on the licensed hosts.