Never Test in Production

Production: The parts of the infrastructure where certain services are executed and serve to its users production

Test environment: A virtual machine running the same configuration as a production environment, but isn’t actually serving any users of the service

Secondary or stand-by machine: A machine that is the same as a production machine, but won’t receive any traffic from actual users until enabled

In this case, once you’ve tested your changes in ​the test environment and are ​ready to deploy them to production, ​first, apply the changes to the secondary machine.  ​Once the changes have been applied, ​make the stand-by machine and primary machine, ​and then apply the changes to the other machine.

Even for the smallest services, ​you should never make changes directly in production. ​Always use a test instance first and only ​deploy the change to production ​after verifying that it works.