SharePoint 2013 "The search service is not able to connect to the machine that hosts the administration component"

Issue

SharePoint Server: 

"The search service is not able to connect to the machine that hosts the administration component" after August 2018 CU

Cause

You need to check the EventViewer after installing August 2018 CU binaries and you can see there is a backward compatibility issue for the Search database if you are applying the patch directly after SP1.

EventViewer Log

"The synchronization operation of the search component: 5a44ee64-4c85-4c9e-a5f6-6098cf079cb1 associated to the search application: Search Service Application on server: DXXXXXV has failed. The component version is not compatible with the search database: SharePoint_Search_AdminDB_CrawlStore on server: DBPROD. The possible cause for this failure is The database schema version is less than the minimum backwards compatibility schema version that is supported for this component. To resolve this problem upgrade this database.."

Resolution

Run the PSConfig and it will upgrade Search databases Schema and which will bring the search up and running.