Upgrading TFE or patching TFE node instances
The mechanism used to upgrade the TFE node instances is to fully repave the instances (destroy and rebuild entirely). This is another reason why using automation to build the instances is important. Currently, the safest way to perform and upgrade is to shut down all node instances, rebuild one node to validate a successful upgrade, and then scale to additional nodes (currently max 3).
Review the Upgrading TFE or Patching TFE Node Instances documentation.