Index and Search Server down after removing broken node or changing topology of Tableau Server

1. Reduce the amount of Index and Search Server search to just one node.
2. Stop tabadminagent on the node with Index and Search Server search.
   Windows: From the services panel, find Tabaminagent and stop the service
   Linux: su to the tableau unprivilged user and disable tabadminagent's service
   - sudo su -l tableau
   - systemctl stop --user tabadminagent_0.service
3. Run below script to disable Index and Search Server search on node
   C:\ProgramData\Tableau\Tableau Server\data\tabsvc\services\indexandsearchserver*\disable.cmd
4. Browse to below location and rename the nodes directory to nodes-old
   C:\ProgramData\Tableau\Tableau Server\data\tabsvc\indexandsearchserver\0\nodes
5. Run below script to start Index and Search Server (You can check in the logs at this point and just ensure that the server is "not initialized"  you can see the following message in the log if it's not initialized - "Not yet initialized (you may need to run sgadmin)" )
   C:\ProgramData\Tableau\Tableau Server\data\tabsvc\services\indexandsearchserver*\enable.cmd (Linux: enable.sh)
6. Run below script to initialize Index and Search Server
   C:\ProgramData\Tableau\Tableau Server\data\tabsvc\services\indexandsearchserver*\data\run-sgadmin.cmd (Linux: run-sgadmin.sh)
7. Start the tabadminagent service.
   Windows: From the services panel, start the Tabadminagent service
   Linux: With the same session as before, run the following command:
   systemctl --user start tabadminagent_0.service
8. Following this, the process should be up. If there are issues loading content in Tableau Server's UI, re-index the search server with this command:
   tsm maintenance reindex-search

Once Tableau Server is back to a running state, add Index and Search Server back to the recommended number of nodes (3 or more).
https://help.tableau.com/current/server/en-us/server_process_index-and-search.htm