The bootstrapper server and web-tier services start and run automatically when you install a web tier. You must start them manually after promoting a replica instance.
The bootstrapper must be running to report web-tier status and to push updates to the web tier. Web-tier services must be running to support web-tier functions such as Self-Service, risk-based authentication (RBA), and dynamic seed provisioning. You can stop, start, and re-start the bootstrapper and web-tier services manually, for example, if you want to stop the web-tier server to migrate to another machine.