Sitecore Upgrade from 8.2 to 10.2

I've worked on a project Upgrade where the first task was to upgrade the existing databases. Here is a list with steps need to be performed

•  Install clean Sitecore 10.2 (for example in "C:\inetpub\wwwroot\sc10sc.dev.local") -  for Developer Workstation -  Graphical setup package for XP Single
• Restore backup DBs (web, core, master) from 8.2 instance 
• Run upgrade scripts (Configuration files for upgrade from  )

• • Script A – CMS_core_master_web8x.sql   - run on Core, Master and Web
  • Script C – CMS_core.sql – Run on Core
  • Script D – CMS_master.sql  - run on Master
  • Script E – CMS_web.sql  - run on Web
  • Script H – CMS_security.sql  - run on Core
• Attach the upgraded DBs to SC 10.2 instance with updating the  ConnectionStrings.config ("C:\inetpub\wwwroot\sc10sc.dev.local\App_Config\ConnectionStrings.config" ) with the new values . For Security connection string point to Core Db.

• Update connection string for Identity Server to match the Core db ("C:\inetpub\wwwroot\sc10identityserver.dev.local\Config\production\Sitecore.IdentityServer.Host.xml")

Clean up the content databases

Sitecore introduces Items as resources. Before , the initial set of OOB items are in the databases. That includes default templates, layouts, workflows etc. Now with 10.1 and after all these are supplied as the resources files outside of database, as files in the file system. They are installed in website\Data folder. With that in mind, the upgraded databases need to be cleaned up. Sitecore creates a tool , called Sitecore.UpdateApp, which is a console app.

In our case, we upgrading from 8.2 Update 3 to 10.2. If you upgrading from different 8.2 version, use the corresponding Package.

• Download Package for 8.2.3 from https://dev.sitecore.net/Downloads/Sitecore%20UpdateApp%20Tool/1x/Sitecore%20UpdateApp%20Tool%20120

• On the Sitecore Launchpad, open the Control Panel, in the Database section, click Clean up databases, select all the databases, and then click Clean.

• Locate the Sitecore.UpdateApp 1.2.0-r0002 for Sitecore 8.2.3 rev. 170407.zip file and  extract its contents to a folder, for example, C:\Sitecore.UpdateApp.

• Copy the license file to the Data folder of the tool, for example, C:\Sitecore.UpdateApp\Data\license.xml.

• In the C:\Sitecore.UpdateApp\App_Config\ConnectionStrings.config file, update the connections to your databases.

• If you do not have a security database, use the connection to the core database.

• Open a Command Prompt in the tool folder and run:

Sitecore.UpdateApp.exe clean

• Clear cache (<instance_url>\sitecore\admin\cache.aspx)